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	$183.84	12.815%	$207.3991	$207.40	$207.40	$207.40
Purchase #2	$119.39	4.472%	$124.7291	$124.73	$124.75	$124.70
Purchase #3	$100.92	10.561%	$111.5782	$111.58	$111.60	$111.60
Purchase #4	$85.27	5.118%	$89.6341	$89.63	$89.65	$89.60
Purchase #5	$29.37	9.529%	$32.1687	$32.17	$32.15	$32.20
Purchase #6	$48.26	12.747%	$54.4117	$54.41	$54.40	$54.40
Purchase #7	$176.76	6.317%	$187.9259	$187.93	$187.95	$187.90
7 purchase totals =	$743.81		$807.8468	$807.85	$807.90	$807.80