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 $47.71   12.385%   $53.6189   $53.62   $53.60   $53.60  
  Purchase #2 $194.84   8.254%   $210.9221   $210.92   $210.90   $210.90  
  Purchase #3 $103.82   13.792%   $118.1389   $118.14   $118.15   $118.10  
  Purchase #4 $18.96   7.684%   $20.4169   $20.42   $20.40   $20.40  
  Purchase #5 $56.28   3.540%   $58.2723   $58.27   $58.25   $58.30  
  Purchase #6 $243.93   5.509%   $257.3681   $257.37   $257.35   $257.40  
  Purchase #7 $200.69   7.838%   $216.4201   $216.42   $216.40   $216.40  
  7 purchase totals = $866.23       $935.1573   $935.16   $935.05   $935.10