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	$91.69	12.778%	$103.4061	$103.41	$103.40	$103.40
Purchase #2	$48.46	4.364%	$50.5748	$50.57	$50.55	$50.60
Purchase #3	$191.42	12.147%	$214.6718	$214.67	$214.65	$214.70
Purchase #4	$18.54	13.655%	$21.0716	$21.07	$21.05	$21.10
Purchase #5	$236.70	4.390%	$247.0911	$247.09	$247.10	$247.10
Purchase #6	$40.77	3.736%	$42.2932	$42.29	$42.30	$42.30
Purchase #7	$138.45	5.316%	$145.81	$145.81	$145.80	$145.80
7 purchase totals =	$766.03		$824.9186	$824.91	$824.85	$825.00