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 $232.26   3.741%   $240.9488   $240.95   $240.95   $240.90  
  Purchase #2 $199.90   10.871%   $221.6311   $221.63   $221.65   $221.60  
  Purchase #3 $155.38   8.277%   $168.2408   $168.24   $168.25   $168.20  
  Purchase #4 $91.46   5.606%   $96.5872   $96.59   $96.60   $96.60  
  Purchase #5 $85.77   3.376%   $88.6656   $88.67   $88.65   $88.70  
  Purchase #6 $132.82   7.792%   $143.1693   $143.17   $143.15   $143.20  
  Purchase #7 $9.84   4.259%   $10.2591   $10.26   $10.25   $10.30  
  7 purchase totals = $907.43       $969.5019   $969.51   $969.50   $969.50