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 $43.96   10.273%   $48.476   $48.48   $48.50   $48.50  
  Purchase #2 $224.89   10.190%   $247.8063   $247.81   $247.80   $247.80  
  Purchase #3 $26.36   8.521%   $28.6061   $28.61   $28.60   $28.60  
  Purchase #4 $213.63   3.521%   $221.1519   $221.15   $221.15   $221.20  
  Purchase #5 $55.79   5.143%   $58.6593   $58.66   $58.65   $58.70  
  Purchase #6 $95.48   3.356%   $98.6843   $98.68   $98.70   $98.70  
  Purchase #7 $105.62   7.394%   $113.4295   $113.43   $113.45   $113.40  
  7 purchase totals = $765.73       $816.8134   $816.82   $816.85   $816.90