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 $248.46   7.709%   $267.6138   $267.61   $267.60   $267.60  
  Purchase #2 $100.89   6.622%   $107.5709   $107.57   $107.55   $107.60  
  Purchase #3 $86.47   8.699%   $93.992   $93.99   $94.00   $94.00  
  Purchase #4 $76.46   13.236%   $86.5802   $86.58   $86.60   $86.60  
  Purchase #5 $233.47   8.497%   $253.3079   $253.31   $253.30   $253.30  
  Purchase #6 $236.74   6.669%   $252.5282   $252.53   $252.55   $252.50  
  Purchase #7 $59.28   11.643%   $66.182   $66.18   $66.20   $66.20  
  7 purchase totals = $1,041.77       $1,127.7750   $1,127.77   $1,127.80   $1,127.80