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 $111.82   11.754%   $124.9633   $124.96   $124.95   $125.00  
  Purchase #2 $200.82   6.244%   $213.3592   $213.36   $213.35   $213.40  
  Purchase #3 $59.28   8.165%   $64.1202   $64.12   $64.10   $64.10  
  Purchase #4 $122.65   10.827%   $135.9293   $135.93   $135.95   $135.90  
  Purchase #5 $74.68   12.387%   $83.9306   $83.93   $83.95   $83.90  
  Purchase #6 $213.64   12.465%   $240.2702   $240.27   $240.25   $240.30  
  Purchase #7 $52.73   8.318%   $57.1161   $57.12   $57.10   $57.10  
  7 purchase totals = $835.62       $919.6889   $919.69   $919.65   $919.70