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	$5.37	7.786%	$5.7881	$5.79	$5.80	$5.80
Purchase #2	$93.46	12.578%	$105.2154	$105.22	$105.20	$105.20
Purchase #3	$38.72	4.483%	$40.4558	$40.46	$40.45	$40.50
Purchase #4	$161.81	7.106%	$173.3082	$173.31	$173.30	$173.30
Purchase #5	$18.85	8.637%	$20.4781	$20.48	$20.50	$20.50
Purchase #6	$249.59	5.325%	$262.8807	$262.88	$262.90	$262.90
Purchase #7	$237.56	4.229%	$247.6064	$247.61	$247.60	$247.60
7 purchase totals =	$805.36		$855.7327	$855.75	$855.75	$855.80