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	$167.57	3.548%	$173.5154	$173.52	$173.50	$173.50
Purchase #2	$101.48	11.460%	$113.1096	$113.11	$113.10	$113.10
Purchase #3	$38.27	11.475%	$42.6615	$42.66	$42.65	$42.70
Purchase #4	$81.61	10.334%	$90.0436	$90.04	$90.05	$90.00
Purchase #5	$127.87	13.103%	$144.6248	$144.62	$144.60	$144.60
Purchase #6	$169.52	3.392%	$175.2701	$175.27	$175.25	$175.30
Purchase #7	$155.26	5.781%	$164.2356	$164.24	$164.25	$164.20
7 purchase totals =	$841.58		$903.4606	$903.46	$903.40	$903.40