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 $22.39   8.273%   $24.2423   $24.24   $24.25   $24.20  
  Purchase #2 $236.86   12.867%   $267.3368   $267.34   $267.35   $267.30  
  Purchase #3 $116.88   13.356%   $132.4905   $132.49   $132.50   $132.50  
  Purchase #4 $95.92   8.296%   $103.8775   $103.88   $103.90   $103.90  
  Purchase #5 $209.69   8.704%   $227.9414   $227.94   $227.95   $227.90  
  Purchase #6 $142.98   12.147%   $160.3478   $160.35   $160.35   $160.30  
  Purchase #7 $130.87   13.638%   $148.7181   $148.72   $148.70   $148.70  
  7 purchase totals = $955.59       $1,064.9544   $1,064.96   $1,065.00   $1,064.80