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 $71.97   6.754%   $76.8309   $76.83   $76.85   $76.80  
  Purchase #2 $61.59   13.338%   $69.8049   $69.80   $69.80   $69.80  
  Purchase #3 $91.31   11.816%   $102.0992   $102.10   $102.10   $102.10  
  Purchase #4 $60.87   13.383%   $69.0162   $69.02   $69.00   $69.00  
  Purchase #5 $27.71   9.337%   $30.2973   $30.30   $30.30   $30.30  
  Purchase #6 $37.63   13.565%   $42.7345   $42.73   $42.75   $42.70  
  Purchase #7 $126.55   11.664%   $141.3108   $141.31   $141.30   $141.30  
  7 purchase totals = $477.63       $532.0938   $532.09   $532.10   $532.00