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	$160.71	12.133%	$180.2089	$180.21	$180.20	$180.20
Purchase #2	$119.98	6.229%	$127.4536	$127.45	$127.45	$127.50
Purchase #3	$136.43	5.273%	$143.624	$143.62	$143.60	$143.60
Purchase #4	$250.28	6.821%	$267.3516	$267.35	$267.35	$267.40
Purchase #5	$238.69	5.213%	$251.1329	$251.13	$251.15	$251.10
Purchase #6	$125.96	4.636%	$131.7995	$131.80	$131.80	$131.80
Purchase #7	$9.57	13.146%	$10.8281	$10.83	$10.85	$10.80
7 purchase totals =	$1,041.62		$1,112.3986	$1,112.39	$1,112.40	$1,112.40