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 $24.55   5.815%   $25.9776   $25.98   $26.00   $26.00  
  Purchase #2 $209.43   12.422%   $235.4454   $235.45   $235.45   $235.40  
  Purchase #3 $71.32   6.259%   $75.7839   $75.78   $75.80   $75.80  
  Purchase #4 $164.84   10.519%   $182.1795   $182.18   $182.20   $182.20  
  Purchase #5 $87.37   7.621%   $94.0285   $94.03   $94.05   $94.00  
  Purchase #6 $93.40   11.463%   $104.1064   $104.11   $104.10   $104.10  
  Purchase #7 $57.63   7.325%   $61.8514   $61.85   $61.85   $61.90  
  7 purchase totals = $708.54       $779.3727   $779.38   $779.45   $779.40