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 $151.61   10.559%   $167.6185   $167.62   $167.60   $167.60  
  Purchase #2 $125.30   5.604%   $132.3218   $132.32   $132.30   $132.30  
  Purchase #3 $132.79   6.634%   $141.5993   $141.60   $141.60   $141.60  
  Purchase #4 $85.52   9.526%   $93.6666   $93.67   $93.65   $93.70  
  Purchase #5 $61.67   13.215%   $69.8197   $69.82   $69.80   $69.80  
  Purchase #6 $70.57   8.506%   $76.5727   $76.57   $76.55   $76.60  
  Purchase #7 $241.43   8.506%   $261.966   $261.97   $261.95   $262.00  
  7 purchase totals = $868.89       $943.5646   $943.57   $943.45   $943.60