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 $55.57   11.416%   $61.9139   $61.91   $61.90   $61.90  
  Purchase #2 $199.82   7.527%   $214.8605   $214.86   $214.85   $214.90  
  Purchase #3 $112.99   4.395%   $117.9559   $117.96   $117.95   $118.00  
  Purchase #4 $248.91   7.375%   $267.2671   $267.27   $267.25   $267.30  
  Purchase #5 $48.35   5.703%   $51.1074   $51.11   $51.10   $51.10  
  Purchase #6 $141.94   13.788%   $161.5107   $161.51   $161.50   $161.50  
  Purchase #7 $48.97   8.130%   $52.9513   $52.95   $52.95   $53.00  
  7 purchase totals = $856.55       $927.5668   $927.57   $927.50   $927.70