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 $112.39   11.408%   $125.2115   $125.21   $125.20   $125.20  
  Purchase #2 $9.39   11.120%   $10.4342   $10.43   $10.45   $10.40  
  Purchase #3 $81.48   3.597%   $84.4108   $84.41   $84.40   $84.40  
  Purchase #4 $218.44   3.871%   $226.8958   $226.90   $226.90   $226.90  
  Purchase #5 $163.45   8.730%   $177.7192   $177.72   $177.70   $177.70  
  Purchase #6 $59.65   11.390%   $66.4441   $66.44   $66.45   $66.40  
  Purchase #7 $110.39   11.442%   $123.0208   $123.02   $123.00   $123.00  
  7 purchase totals = $755.19       $814.1364   $814.13   $814.10   $814.00