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	$154.46	12.327%	$173.5003	$173.50	$173.50	$173.50
Purchase #2	$215.46	10.672%	$238.4539	$238.45	$238.45	$238.50
Purchase #3	$242.96	6.686%	$259.2043	$259.20	$259.20	$259.20
Purchase #4	$109.81	3.468%	$113.6182	$113.62	$113.60	$113.60
Purchase #5	$35.39	13.264%	$40.0841	$40.08	$40.10	$40.10
Purchase #6	$217.73	6.215%	$231.2619	$231.26	$231.25	$231.30
Purchase #7	$68.92	3.257%	$71.1647	$71.16	$71.15	$71.20
7 purchase totals =	$1,044.73		$1,127.2874	$1,127.27	$1,127.25	$1,127.40