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 $61.61   8.240%   $66.6867   $66.69   $66.70   $66.70  
  Purchase #2 $26.51   7.634%   $28.5338   $28.53   $28.55   $28.50  
  Purchase #3 $246.25   12.680%   $277.4745   $277.47   $277.45   $277.50  
  Purchase #4 $47.63   13.667%   $54.1396   $54.14   $54.15   $54.10  
  Purchase #5 $176.94   6.634%   $188.6782   $188.68   $188.70   $188.70  
  Purchase #6 $186.28   6.468%   $198.3286   $198.33   $198.35   $198.30  
  Purchase #7 $92.91   5.189%   $97.7311   $97.73   $97.75   $97.70  
  7 purchase totals = $838.13       $911.5725   $911.57   $911.65   $911.50