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 $46.25   12.382%   $51.9767   $51.98   $52.00   $52.00  
  Purchase #2 $241.42   8.507%   $261.9576   $261.96   $261.95   $262.00  
  Purchase #3 $212.98   13.125%   $240.9336   $240.93   $240.95   $240.90  
  Purchase #4 $148.33   6.415%   $157.8454   $157.85   $157.85   $157.80  
  Purchase #5 $146.56   4.334%   $152.9119   $152.91   $152.90   $152.90  
  Purchase #6 $215.30   5.777%   $227.7379   $227.74   $227.75   $227.70  
  Purchase #7 $146.91   11.265%   $163.4594   $163.46   $163.45   $163.50  
  7 purchase totals = $1,157.75       $1,256.8225   $1,256.83   $1,256.85   $1,256.80