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 $195.80   6.251%   $208.0395   $208.04   $208.05   $208.00  
  Purchase #2 $10.61   5.822%   $11.2277   $11.23   $11.25   $11.20  
  Purchase #3 $89.57   13.126%   $101.327   $101.33   $101.35   $101.30  
  Purchase #4 $101.83   10.858%   $112.8867   $112.89   $112.90   $112.90  
  Purchase #5 $131.96   4.663%   $138.1133   $138.11   $138.10   $138.10  
  Purchase #6 $63.91   10.710%   $70.7548   $70.75   $70.75   $70.80  
  Purchase #7 $146.98   10.170%   $161.9279   $161.93   $161.95   $161.90  
  7 purchase totals = $740.66       $804.2769   $804.28   $804.35   $804.20