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 $67.86   12.867%   $76.5915   $76.59   $76.60   $76.60  
  Purchase #2 $30.54   13.829%   $34.7634   $34.76   $34.75   $34.80  
  Purchase #3 $76.83   9.338%   $84.0044   $84.00   $84.00   $84.00  
  Purchase #4 $127.85   6.380%   $136.0068   $136.01   $136.00   $136.00  
  Purchase #5 $239.77   10.614%   $265.2192   $265.22   $265.20   $265.20  
  Purchase #6 $114.66   9.449%   $125.4942   $125.49   $125.50   $125.50  
  Purchase #7 $209.67   4.803%   $219.7405   $219.74   $219.75   $219.70  
  7 purchase totals = $867.18       $941.8200   $941.81   $941.80   $941.80