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 $57.30   10.591%   $63.3686   $63.37   $63.35   $63.40  
  Purchase #2 $116.61   7.487%   $125.3406   $125.34   $125.35   $125.30  
  Purchase #3 $92.59   7.268%   $99.3194   $99.32   $99.30   $99.30  
  Purchase #4 $134.58   5.131%   $141.4853   $141.49   $141.50   $141.50  
  Purchase #5 $116.81   13.380%   $132.4392   $132.44   $132.45   $132.40  
  Purchase #6 $183.86   13.198%   $208.1258   $208.13   $208.15   $208.10  
  Purchase #7 $119.82   5.774%   $126.7384   $126.74   $126.75   $126.70  
  7 purchase totals = $821.57       $896.8173   $896.83   $896.85   $896.70