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 $68.34   9.414%   $74.7735   $74.77   $74.75   $74.80  
  Purchase #2 $99.56   10.612%   $110.1253   $110.13   $110.15   $110.10  
  Purchase #3 $18.73   3.282%   $19.3447   $19.34   $19.35   $19.30  
  Purchase #4 $237.55   8.866%   $258.6112   $258.61   $258.60   $258.60  
  Purchase #5 $209.61   5.650%   $221.453   $221.45   $221.45   $221.50  
  Purchase #6 $197.56   9.523%   $216.3736   $216.37   $216.35   $216.40  
  Purchase #7 $78.99   5.262%   $83.1465   $83.15   $83.15   $83.10  
  7 purchase totals = $910.34       $983.8278   $983.82   $983.80   $983.80