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 $26.88   10.275%   $29.6419   $29.64   $29.65   $29.60  
  Purchase #2 $186.50   8.632%   $202.5987   $202.60   $202.60   $202.60  
  Purchase #3 $94.81   3.652%   $98.2725   $98.27   $98.25   $98.30  
  Purchase #4 $104.77   13.480%   $118.893   $118.89   $118.90   $118.90  
  Purchase #5 $25.81   8.237%   $27.936   $27.94   $27.95   $27.90  
  Purchase #6 $144.99   9.220%   $158.3581   $158.36   $158.35   $158.40  
  Purchase #7 $107.63   11.484%   $119.9902   $119.99   $120.00   $120.00  
  7 purchase totals = $691.39       $755.6904   $755.69   $755.70   $755.70