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 $215.76   12.567%   $242.8746   $242.87   $242.85   $242.90  
  Purchase #2 $35.75   7.795%   $38.5367   $38.54   $38.55   $38.50  
  Purchase #3 $229.69   13.783%   $261.3482   $261.35   $261.35   $261.30  
  Purchase #4 $54.58   13.230%   $61.8009   $61.80   $61.80   $61.80  
  Purchase #5 $214.95   7.827%   $231.7741   $231.77   $231.75   $231.80  
  Purchase #6 $88.41   4.422%   $92.3195   $92.32   $92.30   $92.30  
  Purchase #7 $120.79   9.548%   $132.323   $132.32   $132.30   $132.30  
  7 purchase totals = $959.93       $1,060.9770   $1,060.97   $1,060.90   $1,060.90