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 $216.99   11.806%   $242.6078   $242.61   $242.60   $242.60  
  Purchase #2 $79.69   3.824%   $82.7373   $82.74   $82.75   $82.70  
  Purchase #3 $210.73   12.122%   $236.2747   $236.27   $236.25   $236.30  
  Purchase #4 $158.74   10.433%   $175.3013   $175.30   $175.30   $175.30  
  Purchase #5 $224.61   8.633%   $244.0006   $244.00   $244.00   $244.00  
  Purchase #6 $170.86   11.542%   $190.5807   $190.58   $190.60   $190.60  
  Purchase #7 $27.54   9.108%   $30.0483   $30.05   $30.05   $30.00  
  7 purchase totals = $1,089.16       $1,201.5507   $1,201.55   $1,201.55   $1,201.50