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	$11.39	9.660%	$12.4903	$12.49	$12.50	$12.50
Purchase #2	$199.28	6.698%	$212.6278	$212.63	$212.65	$212.60
Purchase #3	$13.63	13.713%	$15.4991	$15.50	$15.50	$15.50
Purchase #4	$192.54	12.643%	$216.8828	$216.88	$216.90	$216.90
Purchase #5	$175.55	3.389%	$181.4994	$181.50	$181.50	$181.50
Purchase #6	$233.33	7.363%	$250.5101	$250.51	$250.50	$250.50
Purchase #7	$246.91	10.450%	$272.7121	$272.71	$272.70	$272.70
7 purchase totals =	$1,072.63		$1,162.2216	$1,162.22	$1,162.25	$1,162.20