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	$204.65	12.559%	$230.352	$230.35	$230.35	$230.40
Purchase #2	$12.26	3.713%	$12.7152	$12.72	$12.70	$12.70
Purchase #3	$40.78	5.434%	$42.996	$43.00	$43.00	$43.00
Purchase #4	$205.50	11.155%	$228.4235	$228.42	$228.40	$228.40
Purchase #5	$73.47	9.105%	$80.1594	$80.16	$80.15	$80.20
Purchase #6	$41.63	10.132%	$45.848	$45.85	$45.85	$45.80
Purchase #7	$99.85	9.449%	$109.2848	$109.28	$109.30	$109.30
7 purchase totals =	$678.14		$749.7789	$749.78	$749.75	$749.80