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 $173.53   5.413%   $182.9232   $182.92   $182.90   $182.90  
  Purchase #2 $204.82   5.873%   $216.8491   $216.85   $216.85   $216.80  
  Purchase #3 $171.37   10.530%   $189.4153   $189.42   $189.40   $189.40  
  Purchase #4 $48.68   11.731%   $54.3907   $54.39   $54.40   $54.40  
  Purchase #5 $57.43   11.814%   $64.2148   $64.21   $64.20   $64.20  
  Purchase #6 $46.42   9.752%   $50.9469   $50.95   $50.95   $50.90  
  Purchase #7 $98.94   5.871%   $104.7488   $104.75   $104.75   $104.70  
  7 purchase totals = $801.19       $863.4888   $863.49   $863.45   $863.30