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 $22.93   6.177%   $24.3464   $24.35   $24.35   $24.30  
  Purchase #2 $129.68   8.178%   $140.2852   $140.29   $140.30   $140.30  
  Purchase #3 $230.64   9.512%   $252.5785   $252.58   $252.60   $252.60  
  Purchase #4 $193.59   10.727%   $214.3564   $214.36   $214.35   $214.40  
  Purchase #5 $182.27   10.260%   $200.9709   $200.97   $200.95   $201.00  
  Purchase #6 $151.85   3.286%   $156.8398   $156.84   $156.85   $156.80  
  Purchase #7 $200.69   3.619%   $207.953   $207.95   $207.95   $208.00  
  7 purchase totals = $1,111.65       $1,197.3302   $1,197.34   $1,197.35   $1,197.40