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	$97.80	3.211%	$100.9404	$100.94	$100.95	$100.90
Purchase #2	$243.74	11.241%	$271.1388	$271.14	$271.15	$271.10
Purchase #3	$56.93	3.700%	$59.0364	$59.04	$59.05	$59.00
Purchase #4	$104.39	7.116%	$111.8184	$111.82	$111.80	$111.80
Purchase #5	$44.52	8.833%	$48.4525	$48.45	$48.45	$48.50
Purchase #6	$45.37	12.631%	$51.1007	$51.10	$51.10	$51.10
Purchase #7	$209.96	9.543%	$229.9965	$230.00	$230.00	$230.00
7 purchase totals =	$802.71		$872.4837	$872.49	$872.50	$872.40