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	$195.57	12.582%	$220.1766	$220.18	$220.20	$220.20
Purchase #2	$54.97	7.863%	$59.2923	$59.29	$59.30	$59.30
Purchase #3	$24.25	13.867%	$27.6127	$27.61	$27.60	$27.60
Purchase #4	$97.39	7.233%	$104.4342	$104.43	$104.45	$104.40
Purchase #5	$66.44	11.294%	$73.9437	$73.94	$73.95	$73.90
Purchase #6	$76.61	9.318%	$83.7485	$83.75	$83.75	$83.70
Purchase #7	$156.83	6.167%	$166.5017	$166.50	$166.50	$166.50
7 purchase totals =	$672.06		$735.7097	$735.70	$735.75	$735.60