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 $68.47   11.533%   $76.3666   $76.37   $76.35   $76.40  
  Purchase #2 $140.32   7.870%   $151.3632   $151.36   $151.35   $151.40  
  Purchase #3 $198.46   9.865%   $218.0381   $218.04   $218.05   $218.00  
  Purchase #4 $247.58   5.575%   $261.3826   $261.38   $261.40   $261.40  
  Purchase #5 $152.32   9.594%   $166.9336   $166.93   $166.95   $166.90  
  Purchase #6 $195.58   9.158%   $213.4912   $213.49   $213.50   $213.50  
  Purchase #7 $225.73   7.734%   $243.188   $243.19   $243.20   $243.20  
  7 purchase totals = $1,228.46       $1,330.7633   $1,330.76   $1,330.80   $1,330.80