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 $224.30   13.216%   $253.9435   $253.94   $253.95   $253.90  
  Purchase #2 $64.50   7.651%   $69.4349   $69.43   $69.45   $69.40  
  Purchase #3 $150.79   3.284%   $155.7419   $155.74   $155.75   $155.70  
  Purchase #4 $178.54   11.368%   $198.8364   $198.84   $198.85   $198.80  
  Purchase #5 $134.54   12.274%   $151.0534   $151.05   $151.05   $151.10  
  Purchase #6 $199.76   4.520%   $208.7892   $208.79   $208.80   $208.80  
  Purchase #7 $208.63   4.303%   $217.6073   $217.61   $217.60   $217.60  
  7 purchase totals = $1,161.06       $1,255.4066   $1,255.40   $1,255.45   $1,255.30