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	$47.71	6.729%	$50.9204	$50.92	$50.90	$50.90
Purchase #2	$37.93	7.204%	$40.6625	$40.66	$40.65	$40.70
Purchase #3	$159.52	12.496%	$179.4536	$179.45	$179.45	$179.50
Purchase #4	$82.37	11.803%	$92.0921	$92.09	$92.10	$92.10
Purchase #5	$18.49	10.774%	$20.4821	$20.48	$20.50	$20.50
Purchase #6	$124.28	10.365%	$137.1616	$137.16	$137.15	$137.20
Purchase #7	$46.84	11.802%	$52.3681	$52.37	$52.35	$52.40
7 purchase totals =	$517.14		$573.1404	$573.13	$573.10	$573.30