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 $137.60   4.798%   $144.202   $144.20   $144.20   $144.20  
  Purchase #2 $183.62   6.728%   $195.974   $195.97   $195.95   $196.00  
  Purchase #3 $102.89   13.721%   $117.0075   $117.01   $117.00   $117.00  
  Purchase #4 $184.94   4.802%   $193.8208   $193.82   $193.80   $193.80  
  Purchase #5 $249.95   9.389%   $273.4178   $273.42   $273.40   $273.40  
  Purchase #6 $136.40   10.639%   $150.9116   $150.91   $150.90   $150.90  
  Purchase #7 $186.67   11.381%   $207.9149   $207.91   $207.90   $207.90  
  7 purchase totals = $1,182.07       $1,283.2486   $1,283.24   $1,283.15   $1,283.20