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 $137.89   8.248%   $149.2632   $149.26   $149.25   $149.30  
  Purchase #2 $59.38   5.114%   $62.4167   $62.42   $62.40   $62.40  
  Purchase #3 $59.54   7.853%   $64.2157   $64.22   $64.20   $64.20  
  Purchase #4 $229.47   8.428%   $248.8097   $248.81   $248.80   $248.80  
  Purchase #5 $248.26   7.321%   $266.4351   $266.44   $266.45   $266.40  
  Purchase #6 $244.92   11.685%   $273.5389   $273.54   $273.55   $273.50  
  Purchase #7 $125.79   8.284%   $136.2104   $136.21   $136.20   $136.20  
  7 purchase totals = $1,105.25       $1,200.8897   $1,200.90   $1,200.85   $1,200.80