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 $192.91   4.811%   $202.1909   $202.19   $202.20   $202.20  
  Purchase #2 $83.74   11.185%   $93.1063   $93.11   $93.10   $93.10  
  Purchase #3 $107.45   11.520%   $119.8282   $119.83   $119.85   $119.80  
  Purchase #4 $126.35   4.716%   $132.3087   $132.31   $132.30   $132.30  
  Purchase #5 $92.76   11.593%   $103.5137   $103.51   $103.50   $103.50  
  Purchase #6 $210.54   12.519%   $236.8975   $236.90   $236.90   $236.90  
  Purchase #7 $43.25   3.548%   $44.7845   $44.78   $44.80   $44.80  
  7 purchase totals = $857.00       $932.6298   $932.63   $932.65   $932.60