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	$33.72	4.669%	$35.2944	$35.29	$35.30	$35.30
Purchase #2	$163.83	5.425%	$172.7178	$172.72	$172.70	$172.70
Purchase #3	$74.58	10.641%	$82.5161	$82.52	$82.50	$82.50
Purchase #4	$172.90	9.581%	$189.4655	$189.47	$189.45	$189.50
Purchase #5	$140.30	8.388%	$152.0684	$152.07	$152.05	$152.10
Purchase #6	$124.93	13.271%	$141.5095	$141.51	$141.50	$141.50
Purchase #7	$59.72	11.651%	$66.678	$66.68	$66.70	$66.70
7 purchase totals =	$769.98		$840.2497	$840.26	$840.20	$840.30