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 $10.43   8.628%   $11.3299   $11.33   $11.35   $11.30  
  Purchase #2 $224.63   8.468%   $243.6517   $243.65   $243.65   $243.70  
  Purchase #3 $229.44   12.694%   $258.5651   $258.57   $258.55   $258.60  
  Purchase #4 $35.40   4.209%   $36.89   $36.89   $36.90   $36.90  
  Purchase #5 $217.34   4.626%   $227.3941   $227.39   $227.40   $227.40  
  Purchase #6 $239.50   6.459%   $254.9693   $254.97   $254.95   $255.00  
  Purchase #7 $200.35   8.622%   $217.6242   $217.62   $217.60   $217.60  
  7 purchase totals = $1,157.09       $1,250.4243   $1,250.42   $1,250.40   $1,250.50