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 $122.46   7.599%   $131.7657   $131.77   $131.75   $131.80  
  Purchase #2 $182.60   8.516%   $198.1502   $198.15   $198.15   $198.20  
  Purchase #3 $112.38   9.161%   $122.6751   $122.68   $122.70   $122.70  
  Purchase #4 $188.66   12.240%   $211.752   $211.75   $211.75   $211.80  
  Purchase #5 $107.51   5.249%   $113.1532   $113.15   $113.15   $113.20  
  Purchase #6 $115.67   3.104%   $119.2604   $119.26   $119.25   $119.30  
  Purchase #7 $142.64   10.214%   $157.2092   $157.21   $157.20   $157.20  
  7 purchase totals = $971.92       $1,053.9658   $1,053.97   $1,053.95   $1,054.20