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 $61.77   3.256%   $63.7812   $63.78   $63.80   $63.80  
  Purchase #2 $24.94   6.477%   $26.5554   $26.56   $26.55   $26.60  
  Purchase #3 $192.50   6.105%   $204.2521   $204.25   $204.25   $204.30  
  Purchase #4 $87.94   6.856%   $93.9692   $93.97   $93.95   $94.00  
  Purchase #5 $71.80   13.584%   $81.5533   $81.55   $81.55   $81.60  
  Purchase #6 $51.80   13.856%   $58.9774   $58.98   $59.00   $59.00  
  Purchase #7 $117.43   11.713%   $131.1846   $131.18   $131.20   $131.20  
  7 purchase totals = $608.18       $660.2732   $660.27   $660.30   $660.50