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	$93.82	13.612%	$106.5908	$106.59	$106.60	$106.60
Purchase #2	$71.70	9.472%	$78.4914	$78.49	$78.50	$78.50
Purchase #3	$102.31	3.622%	$106.0157	$106.02	$106.00	$106.00
Purchase #4	$120.57	10.195%	$132.8621	$132.86	$132.85	$132.90
Purchase #5	$46.82	9.546%	$51.2894	$51.29	$51.30	$51.30
Purchase #6	$101.64	3.626%	$105.3255	$105.33	$105.35	$105.30
Purchase #7	$250.56	11.146%	$278.4874	$278.49	$278.50	$278.50
7 purchase totals =	$787.42		$859.0623	$859.07	$859.10	$859.10