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 $242.28   10.462%   $267.6273   $267.63   $267.65   $267.60  
  Purchase #2 $221.98   5.502%   $234.1933   $234.19   $234.20   $234.20  
  Purchase #3 $104.46   13.601%   $118.6676   $118.67   $118.65   $118.70  
  Purchase #4 $41.36   11.362%   $46.0593   $46.06   $46.05   $46.10  
  Purchase #5 $79.77   12.765%   $89.9526   $89.95   $89.95   $90.00  
  Purchase #6 $113.73   3.537%   $117.7526   $117.75   $117.75   $117.80  
  Purchase #7 $87.97   12.125%   $98.6364   $98.64   $98.65   $98.60  
  7 purchase totals = $891.55       $972.8891   $972.89   $972.90   $973.00