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 $185.25   5.391%   $195.2368   $195.24   $195.25   $195.20  
  Purchase #2 $49.46   10.656%   $54.7305   $54.73   $54.75   $54.70  
  Purchase #3 $234.54   11.554%   $261.6388   $261.64   $261.65   $261.60  
  Purchase #4 $13.33   11.781%   $14.9004   $14.90   $14.90   $14.90  
  Purchase #5 $241.77   6.371%   $257.1732   $257.17   $257.15   $257.20  
  Purchase #6 $95.93   4.827%   $100.5605   $100.56   $100.55   $100.60  
  Purchase #7 $64.48   3.239%   $66.5685   $66.57   $66.55   $66.60  
  7 purchase totals = $884.76       $950.8087   $950.81   $950.80   $950.80