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 $248.36   11.671%   $277.3461   $277.35   $277.35   $277.30  
  Purchase #2 $157.84   9.540%   $172.8979   $172.90   $172.90   $172.90  
  Purchase #3 $184.94   12.623%   $208.285   $208.29   $208.30   $208.30  
  Purchase #4 $97.47   10.791%   $107.988   $107.99   $108.00   $108.00  
  Purchase #5 $233.26   3.430%   $241.2608   $241.26   $241.25   $241.30  
  Purchase #6 $131.99   6.766%   $140.9204   $140.92   $140.90   $140.90  
  Purchase #7 $97.73   10.627%   $108.1158   $108.12   $108.10   $108.10  
  7 purchase totals = $1,151.59       $1,256.8140   $1,256.83   $1,256.80   $1,256.80