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 $62.49   6.656%   $66.6493   $66.65   $66.65   $66.60  
  Purchase #2 $206.95   5.187%   $217.6845   $217.68   $217.70   $217.70  
  Purchase #3 $231.69   7.367%   $248.7586   $248.76   $248.75   $248.80  
  Purchase #4 $56.93   8.853%   $61.97   $61.97   $61.95   $62.00  
  Purchase #5 $139.40   12.807%   $157.253   $157.25   $157.25   $157.30  
  Purchase #6 $233.43   4.643%   $244.2682   $244.27   $244.25   $244.30  
  Purchase #7 $21.90   3.405%   $22.6457   $22.65   $22.65   $22.60  
  7 purchase totals = $952.79       $1,019.2293   $1,019.23   $1,019.20   $1,019.30