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 $32.47   9.430%   $35.5319   $35.53   $35.55   $35.50  
  Purchase #2 $238.62   9.476%   $261.2316   $261.23   $261.25   $261.20  
  Purchase #3 $115.62   11.824%   $129.2909   $129.29   $129.30   $129.30  
  Purchase #4 $6.35   7.573%   $6.8309   $6.83   $6.85   $6.80  
  Purchase #5 $95.26   6.869%   $101.8034   $101.80   $101.80   $101.80  
  Purchase #6 $168.29   6.862%   $179.8381   $179.84   $179.85   $179.80  
  Purchase #7 $221.87   3.618%   $229.8973   $229.90   $229.90   $229.90  
  7 purchase totals = $878.48       $944.4241   $944.42   $944.50   $944.30