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	$136.73	4.160%	$142.418	$142.42	$142.40	$142.40
Purchase #2	$155.48	11.741%	$173.7349	$173.73	$173.75	$173.70
Purchase #3	$146.61	8.753%	$159.4428	$159.44	$159.45	$159.40
Purchase #4	$134.67	10.560%	$148.8912	$148.89	$148.90	$148.90
Purchase #5	$53.44	5.140%	$56.1868	$56.19	$56.20	$56.20
Purchase #6	$127.58	9.159%	$139.2651	$139.27	$139.25	$139.30
Purchase #7	$238.44	11.641%	$266.1968	$266.20	$266.20	$266.20
7 purchase totals =	$992.95		$1,086.1356	$1,086.14	$1,086.15	$1,086.10