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 $89.47   7.450%   $96.1355   $96.14   $96.15   $96.10  
  Purchase #2 $103.66   3.484%   $107.2715   $107.27   $107.25   $107.30  
  Purchase #3 $199.65   4.485%   $208.6043   $208.60   $208.60   $208.60  
  Purchase #4 $46.25   7.867%   $49.8885   $49.89   $49.90   $49.90  
  Purchase #5 $101.33   3.338%   $104.7124   $104.71   $104.70   $104.70  
  Purchase #6 $197.59   5.233%   $207.9299   $207.93   $207.95   $207.90  
  Purchase #7 $17.80   9.179%   $19.4339   $19.43   $19.45   $19.40  
  7 purchase totals = $755.75       $793.9760   $793.97   $794.00   $793.90