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 $248.63   7.205%   $266.5438   $266.54   $266.55   $266.50  
  Purchase #2 $214.79   8.136%   $232.2653   $232.27   $232.25   $232.30  
  Purchase #3 $50.92   11.379%   $56.7142   $56.71   $56.70   $56.70  
  Purchase #4 $223.28   13.746%   $253.9721   $253.97   $253.95   $254.00  
  Purchase #5 $169.40   12.641%   $190.8139   $190.81   $190.80   $190.80  
  Purchase #6 $169.82   3.293%   $175.4122   $175.41   $175.40   $175.40  
  Purchase #7 $84.67   9.495%   $92.7094   $92.71   $92.70   $92.70  
  7 purchase totals = $1,161.51       $1,268.4309   $1,268.42   $1,268.35   $1,268.40