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	$103.42	12.632%	$116.484	$116.48	$116.50	$116.50
Purchase #2	$250.73	6.323%	$266.5837	$266.58	$266.60	$266.60
Purchase #3	$132.52	9.727%	$145.4102	$145.41	$145.40	$145.40
Purchase #4	$227.54	11.329%	$253.318	$253.32	$253.30	$253.30
Purchase #5	$125.74	4.699%	$131.6485	$131.65	$131.65	$131.60
Purchase #6	$122.58	8.278%	$132.7272	$132.73	$132.75	$132.70
Purchase #7	$32.30	8.470%	$35.0358	$35.04	$35.05	$35.00
7 purchase totals =	$994.83		$1,081.2074	$1,081.21	$1,081.25	$1,081.10