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 $211.76   7.519%   $227.6822   $227.68   $227.70   $227.70  
  Purchase #2 $87.99   7.313%   $94.4247   $94.42   $94.40   $94.40  
  Purchase #3 $97.66   13.291%   $110.64   $110.64   $110.65   $110.60  
  Purchase #4 $227.63   11.824%   $254.545   $254.55   $254.55   $254.50  
  Purchase #5 $6.72   8.291%   $7.2772   $7.28   $7.30   $7.30  
  Purchase #6 $65.45   6.287%   $69.5648   $69.56   $69.55   $69.60  
  Purchase #7 $125.66   9.701%   $137.8503   $137.85   $137.85   $137.90  
  7 purchase totals = $822.87       $901.9842   $901.98   $902.00   $902.00