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	$127.79	13.711%	$145.3113	$145.31	$145.30	$145.30
Purchase #2	$104.32	5.605%	$110.1671	$110.17	$110.15	$110.20
Purchase #3	$172.86	11.285%	$192.3673	$192.37	$192.35	$192.40
Purchase #4	$192.72	3.451%	$199.3708	$199.37	$199.35	$199.40
Purchase #5	$233.27	12.807%	$263.1449	$263.14	$263.15	$263.10
Purchase #6	$250.30	4.110%	$260.5873	$260.59	$260.60	$260.60
Purchase #7	$99.87	8.613%	$108.4718	$108.47	$108.45	$108.50
7 purchase totals =	$1,181.13		$1,279.4205	$1,279.42	$1,279.35	$1,279.50