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 $241.54   9.828%   $265.2786   $265.28   $265.30   $265.30  
  Purchase #2 $64.59   3.645%   $66.9443   $66.94   $66.95   $66.90  
  Purchase #3 $27.47   7.390%   $29.5   $29.50   $29.50   $29.50  
  Purchase #4 $164.53   10.801%   $182.3009   $182.30   $182.30   $182.30  
  Purchase #5 $218.69   6.422%   $232.7343   $232.73   $232.75   $232.70  
  Purchase #6 $100.96   4.216%   $105.2165   $105.22   $105.20   $105.20  
  Purchase #7 $58.92   9.843%   $64.7195   $64.72   $64.70   $64.70  
  7 purchase totals = $876.70       $946.6941   $946.69   $946.70   $946.60