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	$244.97	11.596%	$273.3767	$273.38	$273.40	$273.40
Purchase #2	$100.37	11.194%	$111.6054	$111.61	$111.60	$111.60
Purchase #3	$190.83	10.625%	$211.1057	$211.11	$211.10	$211.10
Purchase #4	$146.37	3.552%	$151.5691	$151.57	$151.55	$151.60
Purchase #5	$54.59	7.185%	$58.5123	$58.51	$58.50	$58.50
Purchase #6	$223.41	4.399%	$233.2378	$233.24	$233.25	$233.20
Purchase #7	$247.85	6.874%	$264.8872	$264.89	$264.90	$264.90
7 purchase totals =	$1,208.39		$1,304.2942	$1,304.31	$1,304.30	$1,304.30