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	$243.47	12.389%	$273.6335	$273.63	$273.65	$273.60
Purchase #2	$50.84	7.242%	$54.5218	$54.52	$54.50	$54.50
Purchase #3	$64.72	5.462%	$68.255	$68.26	$68.25	$68.30
Purchase #4	$9.88	3.840%	$10.2594	$10.26	$10.25	$10.30
Purchase #5	$107.68	3.667%	$111.6286	$111.63	$111.65	$111.60
Purchase #6	$127.57	3.352%	$131.8461	$131.85	$131.85	$131.80
Purchase #7	$55.85	11.284%	$62.1521	$62.15	$62.15	$62.20
7 purchase totals =	$660.01		$712.2965	$712.30	$712.30	$712.30