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 $119.79   5.471%   $126.3437   $126.34   $126.35   $126.30  
  Purchase #2 $239.85   9.385%   $262.3599   $262.36   $262.35   $262.40  
  Purchase #3 $44.55   5.243%   $46.8858   $46.89   $46.90   $46.90  
  Purchase #4 $181.89   13.657%   $206.7307   $206.73   $206.75   $206.70  
  Purchase #5 $244.33   7.171%   $261.8509   $261.85   $261.85   $261.90  
  Purchase #6 $52.49   3.117%   $54.1261   $54.13   $54.15   $54.10  
  Purchase #7 $23.53   10.222%   $25.9352   $25.94   $25.95   $25.90  
  7 purchase totals = $906.43       $984.2323   $984.24   $984.30   $984.20