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 $60.47   3.859%   $62.8035   $62.80   $62.80   $62.80  
  Purchase #2 $15.62   13.687%   $17.7579   $17.76   $17.75   $17.80  
  Purchase #3 $106.51   12.183%   $119.4861   $119.49   $119.50   $119.50  
  Purchase #4 $101.78   13.764%   $115.789   $115.79   $115.80   $115.80  
  Purchase #5 $236.40   8.393%   $256.2411   $256.24   $256.25   $256.20  
  Purchase #6 $156.63   4.713%   $164.012   $164.01   $164.00   $164.00  
  Purchase #7 $187.26   13.316%   $212.1955   $212.20   $212.20   $212.20  
  7 purchase totals = $864.67       $948.2851   $948.29   $948.30   $948.30