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 $210.60   8.153%   $227.7702   $227.77   $227.75   $227.80  
  Purchase #2 $58.87   6.143%   $62.4864   $62.49   $62.50   $62.50  
  Purchase #3 $67.46   9.106%   $73.6029   $73.60   $73.60   $73.60  
  Purchase #4 $216.69   7.465%   $232.8659   $232.87   $232.85   $232.90  
  Purchase #5 $48.92   8.807%   $53.2284   $53.23   $53.25   $53.20  
  Purchase #6 $197.88   5.823%   $209.4026   $209.40   $209.40   $209.40  
  Purchase #7 $87.39   3.465%   $90.4181   $90.42   $90.40   $90.40  
  7 purchase totals = $887.81       $949.7745   $949.78   $949.75   $949.80