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 $229.93   8.507%   $249.4901   $249.49   $249.50   $249.50  
  Purchase #2 $211.84   10.768%   $234.6509   $234.65   $234.65   $234.70  
  Purchase #3 $233.92   13.555%   $265.6279   $265.63   $265.65   $265.60  
  Purchase #4 $200.82   3.827%   $208.5054   $208.51   $208.50   $208.50  
  Purchase #5 $74.73   11.733%   $83.4981   $83.50   $83.50   $83.50  
  Purchase #6 $184.54   3.682%   $191.3348   $191.33   $191.35   $191.30  
  Purchase #7 $233.96   7.237%   $250.8917   $250.89   $250.90   $250.90  
  7 purchase totals = $1,369.74       $1,483.9989   $1,484.00   $1,484.05   $1,484.00