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 $244.61   6.776%   $261.1848   $261.18   $261.20   $261.20  
  Purchase #2 $25.39   12.453%   $28.5518   $28.55   $28.55   $28.60  
  Purchase #3 $101.51   13.449%   $115.1621   $115.16   $115.15   $115.20  
  Purchase #4 $64.76   10.873%   $71.8014   $71.80   $71.80   $71.80  
  Purchase #5 $165.75   3.141%   $170.9562   $170.96   $170.95   $171.00  
  Purchase #6 $98.36   3.236%   $101.5429   $101.54   $101.55   $101.50  
  Purchase #7 $85.89   7.603%   $92.4202   $92.42   $92.40   $92.40  
  7 purchase totals = $786.27       $841.6194   $841.61   $841.60   $841.70