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 $112.69   12.681%   $126.9802   $126.98   $127.00   $127.00  
  Purchase #2 $154.27   4.200%   $160.7493   $160.75   $160.75   $160.70  
  Purchase #3 $220.42   12.231%   $247.3796   $247.38   $247.40   $247.40  
  Purchase #4 $55.51   4.646%   $58.089   $58.09   $58.10   $58.10  
  Purchase #5 $154.99   5.729%   $163.8694   $163.87   $163.85   $163.90  
  Purchase #6 $116.92   5.228%   $123.0326   $123.03   $123.05   $123.00  
  Purchase #7 $66.99   13.788%   $76.2266   $76.23   $76.25   $76.20  
  7 purchase totals = $881.79       $956.3267   $956.33   $956.40   $956.30