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 $11.42   3.496%   $11.8192   $11.82   $11.80   $11.80  
  Purchase #2 $46.68   4.551%   $48.8044   $48.80   $48.80   $48.80  
  Purchase #3 $166.27   13.186%   $188.1944   $188.19   $188.20   $188.20  
  Purchase #4 $116.27   10.355%   $128.3098   $128.31   $128.30   $128.30  
  Purchase #5 $55.47   5.818%   $58.6972   $58.70   $58.70   $58.70  
  Purchase #6 $181.32   9.788%   $199.0676   $199.07   $199.05   $199.10  
  Purchase #7 $104.58   13.567%   $118.7684   $118.77   $118.75   $118.80  
  7 purchase totals = $682.01       $753.6610   $753.66   $753.60   $753.70