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	$156.34	10.212%	$172.3054	$172.31	$172.30	$172.30
Purchase #2	$26.92	6.433%	$28.6518	$28.65	$28.65	$28.70
Purchase #3	$107.91	3.668%	$111.8681	$111.87	$111.85	$111.90
Purchase #4	$149.42	10.585%	$165.2361	$165.24	$165.25	$165.20
Purchase #5	$52.78	12.262%	$59.2519	$59.25	$59.25	$59.30
Purchase #6	$49.94	3.695%	$51.7853	$51.79	$51.80	$51.80
Purchase #7	$69.74	11.448%	$77.7238	$77.72	$77.70	$77.70
7 purchase totals =	$613.05		$666.8224	$666.83	$666.80	$666.90