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 $183.71   7.754%   $197.9549   $197.95   $197.95   $198.00  
  Purchase #2 $63.88   5.169%   $67.182   $67.18   $67.20   $67.20  
  Purchase #3 $110.51   8.218%   $119.5917   $119.59   $119.60   $119.60  
  Purchase #4 $94.83   10.370%   $104.6639   $104.66   $104.65   $104.70  
  Purchase #5 $47.99   4.427%   $50.1145   $50.11   $50.10   $50.10  
  Purchase #6 $215.68   13.140%   $244.0204   $244.02   $244.00   $244.00  
  Purchase #7 $90.75   13.554%   $103.0503   $103.05   $103.05   $103.10  
  7 purchase totals = $807.35       $886.5777   $886.56   $886.55   $886.70