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 $178.63   12.485%   $200.932   $200.93   $200.95   $200.90  
  Purchase #2 $58.85   11.350%   $65.5295   $65.53   $65.55   $65.50  
  Purchase #3 $216.39   12.308%   $243.0233   $243.02   $243.00   $243.00  
  Purchase #4 $71.51   11.640%   $79.8338   $79.83   $79.85   $79.80  
  Purchase #5 $224.49   10.513%   $248.0906   $248.09   $248.10   $248.10  
  Purchase #6 $67.42   12.186%   $75.6358   $75.64   $75.65   $75.60  
  Purchase #7 $12.63   5.172%   $13.2832   $13.28   $13.30   $13.30  
  7 purchase totals = $829.92       $926.3282   $926.32   $926.40   $926.20