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 $171.56   7.812%   $184.9623   $184.96   $184.95   $185.00  
  Purchase #2 $60.61   6.691%   $64.6654   $64.67   $64.65   $64.70  
  Purchase #3 $224.54   10.859%   $248.9228   $248.92   $248.90   $248.90  
  Purchase #4 $232.66   12.736%   $262.2916   $262.29   $262.30   $262.30  
  Purchase #5 $114.89   13.671%   $130.5966   $130.60   $130.60   $130.60  
  Purchase #6 $65.86   6.247%   $69.9743   $69.97   $69.95   $70.00  
  Purchase #7 $208.65   10.609%   $230.7857   $230.79   $230.80   $230.80  
  7 purchase totals = $1,078.77       $1,192.1987   $1,192.20   $1,192.15   $1,192.30