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	$11.71	5.599%	$12.3656	$12.37	$12.35	$12.40
Purchase #2	$172.52	8.641%	$187.4275	$187.43	$187.45	$187.40
Purchase #3	$40.48	11.312%	$45.0591	$45.06	$45.05	$45.10
Purchase #4	$226.76	3.282%	$234.2023	$234.20	$234.20	$234.20
Purchase #5	$242.54	3.321%	$250.5948	$250.59	$250.60	$250.60
Purchase #6	$98.41	4.695%	$103.0303	$103.03	$103.05	$103.00
Purchase #7	$164.91	12.461%	$185.4594	$185.46	$185.45	$185.50
7 purchase totals =	$957.33		$1,018.1390	$1,018.14	$1,018.15	$1,018.20