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	$12.55	7.285%	$13.4643	$13.46	$13.45	$13.50
Purchase #2	$118.66	7.757%	$127.8645	$127.86	$127.85	$127.90
Purchase #3	$131.83	11.719%	$147.2792	$147.28	$147.30	$147.30
Purchase #4	$231.40	9.828%	$254.142	$254.14	$254.15	$254.10
Purchase #5	$214.73	4.520%	$224.4358	$224.44	$224.45	$224.40
Purchase #6	$24.73	9.440%	$27.0645	$27.06	$27.05	$27.10
Purchase #7	$173.40	6.210%	$184.1681	$184.17	$184.15	$184.20
7 purchase totals =	$907.30		$978.4184	$978.41	$978.40	$978.50