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 $61.95   7.176%   $66.3955   $66.40   $66.40   $66.40  
  Purchase #2 $211.55   6.183%   $224.6301   $224.63   $224.65   $224.60  
  Purchase #3 $15.76   4.462%   $16.4632   $16.46   $16.45   $16.50  
  Purchase #4 $13.76   6.369%   $14.6364   $14.64   $14.65   $14.60  
  Purchase #5 $194.33   3.468%   $201.0694   $201.07   $201.05   $201.10  
  Purchase #6 $206.96   5.302%   $217.933   $217.93   $217.95   $217.90  
  Purchase #7 $140.33   8.255%   $151.9142   $151.91   $151.90   $151.90  
  7 purchase totals = $844.64       $893.0418   $893.04   $893.05   $893.00