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 $183.41   12.643%   $206.5985   $206.60   $206.60   $206.60  
  Purchase #2 $157.63   13.120%   $178.3111   $178.31   $178.30   $178.30  
  Purchase #3 $109.64   4.501%   $114.5749   $114.57   $114.55   $114.60  
  Purchase #4 $62.99   5.596%   $66.5149   $66.51   $66.50   $66.50  
  Purchase #5 $75.64   13.371%   $85.7538   $85.75   $85.75   $85.80  
  Purchase #6 $149.53   13.590%   $169.8511   $169.85   $169.85   $169.90  
  Purchase #7 $57.50   5.206%   $60.4935   $60.49   $60.50   $60.50  
  7 purchase totals = $796.34       $882.0978   $882.08   $882.05   $882.20