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	$178.70	11.443%	$199.1486	$199.15	$199.15	$199.10
Purchase #2	$14.31	6.362%	$15.2204	$15.22	$15.20	$15.20
Purchase #3	$232.99	12.594%	$262.3328	$262.33	$262.35	$262.30
Purchase #4	$139.68	7.113%	$149.6154	$149.62	$149.60	$149.60
Purchase #5	$29.41	13.860%	$33.4862	$33.49	$33.50	$33.50
Purchase #6	$114.66	10.866%	$127.119	$127.12	$127.10	$127.10
Purchase #7	$30.29	9.224%	$33.0839	$33.08	$33.10	$33.10
7 purchase totals =	$740.04		$820.0063	$820.01	$820.00	$819.90