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 $23.65   8.859%   $25.7452   $25.75   $25.75   $25.70  
  Purchase #2 $42.68   9.114%   $46.5699   $46.57   $46.55   $46.60  
  Purchase #3 $235.98   8.256%   $255.4625   $255.46   $255.45   $255.50  
  Purchase #4 $177.38   7.255%   $190.2489   $190.25   $190.25   $190.20  
  Purchase #5 $53.36   6.491%   $56.8236   $56.82   $56.80   $56.80  
  Purchase #6 $156.92   9.573%   $171.942   $171.94   $171.95   $171.90  
  Purchase #7 $22.46   4.198%   $23.4029   $23.40   $23.40   $23.40  
  7 purchase totals = $712.43       $770.1950   $770.19   $770.15   $770.10