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 $245.46   8.772%   $266.9918   $266.99   $267.00   $267.00  
  Purchase #2 $172.42   13.706%   $196.0519   $196.05   $196.05   $196.10  
  Purchase #3 $57.59   5.810%   $60.936   $60.94   $60.95   $60.90  
  Purchase #4 $14.62   9.808%   $16.0539   $16.05   $16.05   $16.10  
  Purchase #5 $183.92   8.719%   $199.956   $199.96   $199.95   $200.00  
  Purchase #6 $114.95   10.588%   $127.1209   $127.12   $127.10   $127.10  
  Purchase #7 $241.40   11.451%   $269.0427   $269.04   $269.05   $269.00  
  7 purchase totals = $1,030.36       $1,136.1532   $1,136.15   $1,136.15   $1,136.20