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 $159.34   4.655%   $166.7573   $166.76   $166.75   $166.80  
  Purchase #2 $125.98   3.225%   $130.0429   $130.04   $130.05   $130.00  
  Purchase #3 $205.92   4.783%   $215.7692   $215.77   $215.75   $215.80  
  Purchase #4 $212.94   9.868%   $233.9529   $233.95   $233.95   $234.00  
  Purchase #5 $41.31   13.671%   $46.9575   $46.96   $46.95   $47.00  
  Purchase #6 $158.70   9.209%   $173.3147   $173.31   $173.30   $173.30  
  Purchase #7 $47.49   4.636%   $49.6916   $49.69   $49.70   $49.70  
  7 purchase totals = $951.68       $1,016.4861   $1,016.48   $1,016.45   $1,016.60