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 $72.40   5.181%   $76.151   $76.15   $76.15   $76.20  
  Purchase #2 $245.95   12.695%   $277.1734   $277.17   $277.15   $277.20  
  Purchase #3 $236.39   10.821%   $261.9698   $261.97   $261.95   $262.00  
  Purchase #4 $29.79   13.453%   $33.7976   $33.80   $33.80   $33.80  
  Purchase #5 $5.76   6.801%   $6.1517   $6.15   $6.15   $6.20  
  Purchase #6 $127.89   5.678%   $135.1516   $135.15   $135.15   $135.20  
  Purchase #7 $244.31   3.578%   $253.0514   $253.05   $253.05   $253.10  
  7 purchase totals = $962.49       $1,043.4465   $1,043.44   $1,043.40   $1,043.70