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 $56.68   10.702%   $62.7459   $62.75   $62.75   $62.70  
  Purchase #2 $59.27   4.393%   $61.8737   $61.87   $61.85   $61.90  
  Purchase #3 $160.34   8.681%   $174.2591   $174.26   $174.25   $174.30  
  Purchase #4 $186.44   13.127%   $210.914   $210.91   $210.90   $210.90  
  Purchase #5 $135.71   10.357%   $149.7655   $149.77   $149.75   $149.80  
  Purchase #6 $67.64   6.573%   $72.086   $72.09   $72.10   $72.10  
  Purchase #7 $194.63   5.253%   $204.8539   $204.85   $204.85   $204.90  
  7 purchase totals = $860.71       $936.4981   $936.50   $936.45   $936.60