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 $63.99   8.686%   $69.5482   $69.55   $69.55   $69.50  
  Purchase #2 $94.77   9.585%   $103.8537   $103.85   $103.85   $103.90  
  Purchase #3 $24.80   11.209%   $27.5798   $27.58   $27.60   $27.60  
  Purchase #4 $188.56   11.571%   $210.3783   $210.38   $210.40   $210.40  
  Purchase #5 $33.64   9.735%   $36.9149   $36.91   $36.90   $36.90  
  Purchase #6 $154.87   6.214%   $164.4936   $164.49   $164.50   $164.50  
  Purchase #7 $116.68   7.253%   $125.1428   $125.14   $125.15   $125.10  
  7 purchase totals = $677.31       $737.9113   $737.90   $737.95   $737.90