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 $68.32   11.675%   $76.2964   $76.30   $76.30   $76.30  
  Purchase #2 $224.82   9.223%   $245.5551   $245.56   $245.55   $245.60  
  Purchase #3 $92.63   13.287%   $104.9377   $104.94   $104.95   $104.90  
  Purchase #4 $119.42   8.219%   $129.2351   $129.24   $129.25   $129.20  
  Purchase #5 $27.76   5.190%   $29.2007   $29.20   $29.20   $29.20  
  Purchase #6 $144.47   10.339%   $159.4068   $159.41   $159.40   $159.40  
  Purchase #7 $74.35   11.636%   $83.0014   $83.00   $83.00   $83.00  
  7 purchase totals = $751.77       $827.6332   $827.65   $827.65   $827.60