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 $56.26   3.681%   $58.3309   $58.33   $58.35   $58.30  
  Purchase #2 $91.65   8.651%   $99.5786   $99.58   $99.60   $99.60  
  Purchase #3 $244.25   11.589%   $272.5561   $272.56   $272.55   $272.60  
  Purchase #4 $108.47   4.423%   $113.2676   $113.27   $113.25   $113.30  
  Purchase #5 $113.43   10.172%   $124.9681   $124.97   $124.95   $125.00  
  Purchase #6 $65.56   5.627%   $69.2491   $69.25   $69.25   $69.20  
  Purchase #7 $85.89   9.405%   $93.968   $93.97   $93.95   $94.00  
  7 purchase totals = $765.51       $831.9184   $831.93   $831.90   $832.00