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 $221.47   8.193%   $239.615   $239.62   $239.60   $239.60  
  Purchase #2 $88.35   6.134%   $93.7694   $93.77   $93.75   $93.80  
  Purchase #3 $73.79   3.611%   $76.4546   $76.45   $76.45   $76.50  
  Purchase #4 $199.27   13.209%   $225.5916   $225.59   $225.60   $225.60  
  Purchase #5 $94.59   6.841%   $101.0609   $101.06   $101.05   $101.10  
  Purchase #6 $19.92   13.595%   $22.6281   $22.63   $22.65   $22.60  
  Purchase #7 $123.74   9.381%   $135.348   $135.35   $135.35   $135.30  
  7 purchase totals = $821.13       $894.4676   $894.47   $894.45   $894.50