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 $32.73   5.778%   $34.6211   $34.62   $34.60   $34.60  
  Purchase #2 $94.42   13.784%   $107.4349   $107.43   $107.45   $107.40  
  Purchase #3 $69.56   5.565%   $73.431   $73.43   $73.45   $73.40  
  Purchase #4 $231.60   12.594%   $260.7677   $260.77   $260.75   $260.80  
  Purchase #5 $71.28   10.365%   $78.6682   $78.67   $78.65   $78.70  
  Purchase #6 $197.64   6.157%   $209.8087   $209.81   $209.80   $209.80  
  Purchase #7 $124.63   7.628%   $134.1368   $134.14   $134.15   $134.10  
  7 purchase totals = $821.86       $898.8684   $898.87   $898.85   $898.80