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	$242.73	12.537%	$273.1611	$273.16	$273.15	$273.20
Purchase #2	$35.56	8.172%	$38.466	$38.47	$38.45	$38.50
Purchase #3	$20.78	8.429%	$22.5315	$22.53	$22.55	$22.50
Purchase #4	$185.36	4.500%	$193.7012	$193.70	$193.70	$193.70
Purchase #5	$10.89	4.479%	$11.3778	$11.38	$11.40	$11.40
Purchase #6	$43.36	5.751%	$45.8536	$45.85	$45.85	$45.90
Purchase #7	$209.82	3.485%	$217.1322	$217.13	$217.15	$217.10
7 purchase totals =	$748.50		$802.2234	$802.22	$802.25	$802.30