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	$237.60	13.467%	$269.5976	$269.60	$269.60	$269.60
Purchase #2	$195.42	10.102%	$215.1613	$215.16	$215.15	$215.20
Purchase #3	$107.35	13.402%	$121.737	$121.74	$121.75	$121.70
Purchase #4	$214.87	3.676%	$222.7686	$222.77	$222.75	$222.80
Purchase #5	$145.41	13.335%	$164.8004	$164.80	$164.80	$164.80
Purchase #6	$40.96	4.756%	$42.9081	$42.91	$42.90	$42.90
Purchase #7	$45.92	12.174%	$51.5103	$51.51	$51.50	$51.50
7 purchase totals =	$987.53		$1,088.4833	$1,088.49	$1,088.45	$1,088.50