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	$232.73	12.104%	$260.8996	$260.90	$260.90	$260.90
Purchase #2	$22.55	3.238%	$23.2802	$23.28	$23.30	$23.30
Purchase #3	$105.82	3.117%	$109.1184	$109.12	$109.10	$109.10
Purchase #4	$190.95	13.653%	$217.0204	$217.02	$217.00	$217.00
Purchase #5	$81.30	11.259%	$90.4536	$90.45	$90.45	$90.50
Purchase #6	$141.84	8.223%	$153.5035	$153.50	$153.50	$153.50
Purchase #7	$102.83	6.150%	$109.154	$109.15	$109.15	$109.20
7 purchase totals =	$878.02		$963.4297	$963.42	$963.40	$963.50