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 $249.64   7.633%   $268.695   $268.70   $268.70   $268.70  
  Purchase #2 $32.40   4.694%   $33.9209   $33.92   $33.90   $33.90  
  Purchase #3 $89.45   10.158%   $98.5363   $98.54   $98.55   $98.50  
  Purchase #4 $218.82   13.474%   $248.3038   $248.30   $248.30   $248.30  
  Purchase #5 $6.25   12.513%   $7.0321   $7.03   $7.05   $7.00  
  Purchase #6 $221.32   12.488%   $248.9584   $248.96   $248.95   $249.00  
  Purchase #7 $167.70   9.219%   $183.1603   $183.16   $183.15   $183.20  
  7 purchase totals = $985.58       $1,088.6068   $1,088.61   $1,088.60   $1,088.60