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 $208.56   13.190%   $236.0691   $236.07   $236.05   $236.10  
  Purchase #2 $76.29   12.866%   $86.1055   $86.11   $86.10   $86.10  
  Purchase #3 $167.57   5.591%   $176.9388   $176.94   $176.95   $176.90  
  Purchase #4 $118.31   12.282%   $132.8408   $132.84   $132.85   $132.80  
  Purchase #5 $13.73   11.752%   $15.3435   $15.34   $15.35   $15.30  
  Purchase #6 $62.59   12.331%   $70.308   $70.31   $70.30   $70.30  
  Purchase #7 $95.99   10.389%   $105.9624   $105.96   $105.95   $106.00  
  7 purchase totals = $743.04       $823.5681   $823.57   $823.55   $823.50