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 $244.64   6.626%   $260.8498   $260.85   $260.85   $260.80  
  Purchase #2 $159.54   5.507%   $168.3259   $168.33   $168.35   $168.30  
  Purchase #3 $239.86   9.132%   $261.764   $261.76   $261.75   $261.80  
  Purchase #4 $152.97   7.614%   $164.6171   $164.62   $164.60   $164.60  
  Purchase #5 $89.96   5.246%   $94.6793   $94.68   $94.70   $94.70  
  Purchase #6 $226.34   6.763%   $241.6474   $241.65   $241.65   $241.60  
  Purchase #7 $59.56   11.746%   $66.5559   $66.56   $66.55   $66.60  
  7 purchase totals = $1,172.87       $1,258.4394   $1,258.45   $1,258.45   $1,258.40