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	$250.31	13.510%	$284.1269	$284.13	$284.15	$284.10
Purchase #2	$161.30	11.764%	$180.2753	$180.28	$180.30	$180.30
Purchase #3	$20.95	7.343%	$22.4884	$22.49	$22.50	$22.50
Purchase #4	$156.88	10.313%	$173.059	$173.06	$173.05	$173.10
Purchase #5	$112.50	13.284%	$127.4445	$127.44	$127.45	$127.40
Purchase #6	$16.91	7.207%	$18.1287	$18.13	$18.15	$18.10
Purchase #7	$232.65	5.571%	$245.6109	$245.61	$245.60	$245.60
7 purchase totals =	$951.50		$1,051.1337	$1,051.14	$1,051.20	$1,051.10