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 $81.58   13.402%   $92.5134   $92.51   $92.50   $92.50  
  Purchase #2 $237.46   9.425%   $259.8406   $259.84   $259.85   $259.80  
  Purchase #3 $115.36   7.216%   $123.6844   $123.68   $123.70   $123.70  
  Purchase #4 $245.91   12.532%   $276.7274   $276.73   $276.75   $276.70  
  Purchase #5 $17.92   6.370%   $19.0615   $19.06   $19.05   $19.10  
  Purchase #6 $47.80   9.338%   $52.2636   $52.26   $52.25   $52.30  
  Purchase #7 $119.90   10.596%   $132.6046   $132.60   $132.60   $132.60  
  7 purchase totals = $865.93       $956.6955   $956.68   $956.70   $956.70