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 $58.55   13.697%   $66.5696   $66.57   $66.55   $66.60  
  Purchase #2 $126.49   4.539%   $132.2314   $132.23   $132.25   $132.20  
  Purchase #3 $156.30   10.105%   $172.0941   $172.09   $172.10   $172.10  
  Purchase #4 $247.76   13.800%   $281.9509   $281.95   $281.95   $282.00  
  Purchase #5 $140.50   3.163%   $144.944   $144.94   $144.95   $144.90  
  Purchase #6 $240.91   9.405%   $263.5676   $263.57   $263.55   $263.60  
  Purchase #7 $175.83   9.716%   $192.9136   $192.91   $192.90   $192.90  
  7 purchase totals = $1,146.34       $1,254.2712   $1,254.26   $1,254.25   $1,254.30