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	$233.40	11.204%	$259.5501	$259.55	$259.55	$259.60
Purchase #2	$194.62	13.103%	$220.1211	$220.12	$220.10	$220.10
Purchase #3	$50.89	10.487%	$56.2268	$56.23	$56.25	$56.20
Purchase #4	$236.43	11.199%	$262.9078	$262.91	$262.90	$262.90
Purchase #5	$10.45	6.444%	$11.1234	$11.12	$11.10	$11.10
Purchase #6	$203.82	10.428%	$225.0743	$225.07	$225.05	$225.10
Purchase #7	$181.94	4.139%	$189.4705	$189.47	$189.45	$189.50
7 purchase totals =	$1,111.55		$1,224.4740	$1,224.47	$1,224.40	$1,224.50