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	$90.65	10.313%	$99.9987	$100.00	$100.00	$100.00
Purchase #2	$141.42	7.851%	$152.5229	$152.52	$152.50	$152.50
Purchase #3	$75.60	4.171%	$78.7533	$78.75	$78.75	$78.80
Purchase #4	$148.47	3.801%	$154.1133	$154.11	$154.10	$154.10
Purchase #5	$164.91	6.445%	$175.5384	$175.54	$175.55	$175.50
Purchase #6	$165.66	10.694%	$183.3757	$183.38	$183.40	$183.40
Purchase #7	$46.36	8.252%	$50.1856	$50.19	$50.20	$50.20
7 purchase totals =	$833.07		$894.4879	$894.49	$894.50	$894.50