Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $126.53   12.217%   $141.9882   $141.99   $142.00   $142.00  
  Purchase #2 $165.94   11.496%   $185.0165   $185.02   $185.00   $185.00  
  Purchase #3 $156.89   10.756%   $173.7651   $173.77   $173.75   $173.80  
  Purchase #4 $226.85   8.608%   $246.3772   $246.38   $246.40   $246.40  
  Purchase #5 $211.38   10.319%   $233.1923   $233.19   $233.20   $233.20  
  Purchase #6 $242.46   12.225%   $272.1007   $272.10   $272.10   $272.10  
  Purchase #7 $212.42   13.496%   $241.0882   $241.09   $241.10   $241.10  
  7 purchase totals = $1,342.47       $1,493.5282   $1,493.54   $1,493.55   $1,493.60