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	$141.98	7.634%	$152.8188	$152.82	$152.80	$152.80
Purchase #2	$30.55	11.149%	$33.956	$33.96	$33.95	$34.00
Purchase #3	$85.75	7.783%	$92.4239	$92.42	$92.40	$92.40
Purchase #4	$82.96	9.103%	$90.5118	$90.51	$90.50	$90.50
Purchase #5	$246.25	10.260%	$271.5153	$271.52	$271.50	$271.50
Purchase #6	$20.33	13.681%	$23.1113	$23.11	$23.10	$23.10
Purchase #7	$230.28	9.365%	$251.8457	$251.85	$251.85	$251.80
7 purchase totals =	$838.10		$916.1828	$916.19	$916.10	$916.10