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 $188.36   3.448%   $194.8547   $194.85   $194.85   $194.90  
  Purchase #2 $178.93   7.667%   $192.6486   $192.65   $192.65   $192.60  
  Purchase #3 $119.76   3.716%   $124.2103   $124.21   $124.20   $124.20  
  Purchase #4 $22.87   8.111%   $24.725   $24.73   $24.75   $24.70  
  Purchase #5 $143.31   10.441%   $158.273   $158.27   $158.25   $158.30  
  Purchase #6 $58.27   12.262%   $65.4151   $65.42   $65.40   $65.40  
  Purchase #7 $192.47   11.588%   $214.7734   $214.77   $214.75   $214.80  
  7 purchase totals = $903.97       $974.9001   $974.90   $974.85   $974.90