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	$148.87	11.857%	$166.5215	$166.52	$166.50	$166.50
Purchase #2	$171.33	7.583%	$184.322	$184.32	$184.30	$184.30
Purchase #3	$205.32	12.203%	$230.3752	$230.38	$230.40	$230.40
Purchase #4	$196.51	11.244%	$218.6056	$218.61	$218.60	$218.60
Purchase #5	$65.43	6.556%	$69.7196	$69.72	$69.70	$69.70
Purchase #6	$101.53	5.260%	$106.8705	$106.87	$106.85	$106.90
Purchase #7	$91.75	3.635%	$95.0851	$95.09	$95.10	$95.10
7 purchase totals =	$980.74		$1,071.4995	$1,071.51	$1,071.45	$1,071.50