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 $182.25   13.655%   $207.1362   $207.14   $207.15   $207.10  
  Purchase #2 $151.72   9.633%   $166.3352   $166.34   $166.35   $166.30  
  Purchase #3 $180.69   7.216%   $193.7286   $193.73   $193.75   $193.70  
  Purchase #4 $241.38   8.843%   $262.7252   $262.73   $262.75   $262.70  
  Purchase #5 $152.57   5.837%   $161.4755   $161.48   $161.50   $161.50  
  Purchase #6 $40.46   5.664%   $42.7517   $42.75   $42.75   $42.80  
  Purchase #7 $209.25   8.873%   $227.8168   $227.82   $227.80   $227.80  
  7 purchase totals = $1,158.32       $1,261.9692   $1,261.99   $1,262.05   $1,261.90