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 $233.91   8.184%   $253.0532   $253.05   $253.05   $253.10  
  Purchase #2 $213.91   13.143%   $242.0242   $242.02   $242.00   $242.00  
  Purchase #3 $85.69   12.464%   $96.3704   $96.37   $96.35   $96.40  
  Purchase #4 $173.46   11.210%   $192.9049   $192.90   $192.90   $192.90  
  Purchase #5 $113.69   4.262%   $118.5355   $118.54   $118.55   $118.50  
  Purchase #6 $240.42   10.267%   $265.1039   $265.10   $265.10   $265.10  
  Purchase #7 $76.77   6.743%   $81.9466   $81.95   $81.95   $81.90  
  7 purchase totals = $1,137.85       $1,249.9387   $1,249.93   $1,249.90   $1,249.90