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 $215.35   11.755%   $240.6644   $240.66   $240.65   $240.70  
  Purchase #2 $164.65   5.377%   $173.5032   $173.50   $173.50   $173.50  
  Purchase #3 $109.64   4.177%   $114.2197   $114.22   $114.20   $114.20  
  Purchase #4 $167.70   3.250%   $173.1503   $173.15   $173.15   $173.20  
  Purchase #5 $189.31   9.185%   $206.6981   $206.70   $206.70   $206.70  
  Purchase #6 $19.66   11.721%   $21.9643   $21.96   $21.95   $22.00  
  Purchase #7 $118.30   10.742%   $131.0078   $131.01   $131.00   $131.00  
  7 purchase totals = $984.61       $1,061.2078   $1,061.20   $1,061.15   $1,061.30