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	$146.72	12.585%	$165.1847	$165.18	$165.20	$165.20
Purchase #2	$65.84	6.319%	$70.0004	$70.00	$70.00	$70.00
Purchase #3	$180.38	9.137%	$196.8613	$196.86	$196.85	$196.90
Purchase #4	$54.85	10.150%	$60.4173	$60.42	$60.40	$60.40
Purchase #5	$83.52	13.408%	$94.7184	$94.72	$94.70	$94.70
Purchase #6	$232.54	8.309%	$251.8617	$251.86	$251.85	$251.90
Purchase #7	$230.25	6.161%	$244.4357	$244.44	$244.45	$244.40
7 purchase totals =	$994.10		$1,083.4795	$1,083.48	$1,083.45	$1,083.50