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	$120.72	12.685%	$136.0333	$136.03	$136.05	$136.00
Purchase #2	$129.77	5.267%	$136.605	$136.61	$136.60	$136.60
Purchase #3	$180.34	11.238%	$200.6066	$200.61	$200.60	$200.60
Purchase #4	$167.34	3.150%	$172.6112	$172.61	$172.60	$172.60
Purchase #5	$120.40	5.687%	$127.2471	$127.25	$127.25	$127.20
Purchase #6	$15.58	7.694%	$16.7787	$16.78	$16.80	$16.80
Purchase #7	$198.93	9.331%	$217.4922	$217.49	$217.50	$217.50
7 purchase totals =	$933.08		$1,007.3741	$1,007.38	$1,007.40	$1,007.30