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 $94.95   3.376%   $98.1555   $98.16   $98.15   $98.20  
  Purchase #2 $21.99   6.668%   $23.4563   $23.46   $23.45   $23.50  
  Purchase #3 $20.97   7.188%   $22.4773   $22.48   $22.50   $22.50  
  Purchase #4 $211.92   13.473%   $240.472   $240.47   $240.45   $240.50  
  Purchase #5 $48.32   13.657%   $54.9191   $54.92   $54.90   $54.90  
  Purchase #6 $156.59   6.790%   $167.2225   $167.22   $167.20   $167.20  
  Purchase #7 $200.65   4.636%   $209.9521   $209.95   $209.95   $210.00  
  7 purchase totals = $755.39       $816.6548   $816.66   $816.60   $816.80