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 $61.63   8.739%   $67.0158   $67.02   $67.00   $67.00  
  Purchase #2 $124.46   6.626%   $132.7067   $132.71   $132.70   $132.70  
  Purchase #3 $113.63   5.321%   $119.6763   $119.68   $119.70   $119.70  
  Purchase #4 $225.65   13.854%   $256.9116   $256.91   $256.90   $256.90  
  Purchase #5 $179.86   3.253%   $185.7108   $185.71   $185.70   $185.70  
  Purchase #6 $109.65   7.412%   $117.7773   $117.78   $117.80   $117.80  
  Purchase #7 $237.58   5.602%   $250.8892   $250.89   $250.90   $250.90  
  7 purchase totals = $1,052.46       $1,130.6877   $1,130.70   $1,130.70   $1,130.70