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 $51.97   7.679%   $55.9608   $55.96   $55.95   $56.00  
  Purchase #2 $144.79   6.793%   $154.6256   $154.63   $154.65   $154.60  
  Purchase #3 $228.77   3.410%   $236.5711   $236.57   $236.55   $236.60  
  Purchase #4 $190.61   9.187%   $208.1213   $208.12   $208.10   $208.10  
  Purchase #5 $66.43   11.352%   $73.9711   $73.97   $73.95   $74.00  
  Purchase #6 $69.25   3.166%   $71.4425   $71.44   $71.45   $71.40  
  Purchase #7 $180.79   3.664%   $187.4141   $187.41   $187.40   $187.40  
  7 purchase totals = $932.61       $988.1065   $988.10   $988.05   $988.10