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 $58.38   10.491%   $64.5046   $64.50   $64.50   $64.50  
  Purchase #2 $171.67   11.245%   $190.9743   $190.97   $190.95   $191.00  
  Purchase #3 $212.50   12.162%   $238.3443   $238.34   $238.35   $238.30  
  Purchase #4 $29.92   8.607%   $32.4952   $32.50   $32.50   $32.50  
  Purchase #5 $191.31   11.792%   $213.8693   $213.87   $213.85   $213.90  
  Purchase #6 $21.94   8.490%   $23.8027   $23.80   $23.80   $23.80  
  Purchase #7 $96.58   4.567%   $100.9908   $100.99   $101.00   $101.00  
  7 purchase totals = $782.30       $864.9812   $864.97   $864.95   $865.00