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	$33.58	4.865%	$35.2137	$35.21	$35.20	$35.20
Purchase #2	$56.40	5.856%	$59.7028	$59.70	$59.70	$59.70
Purchase #3	$127.54	3.430%	$131.9146	$131.91	$131.90	$131.90
Purchase #4	$62.39	6.621%	$66.5208	$66.52	$66.50	$66.50
Purchase #5	$200.68	10.537%	$221.8257	$221.83	$221.85	$221.80
Purchase #6	$59.27	8.271%	$64.1722	$64.17	$64.15	$64.20
Purchase #7	$82.65	8.210%	$89.4356	$89.44	$89.45	$89.40
7 purchase totals =	$622.51		$668.7854	$668.78	$668.75	$668.70