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	$150.55	10.362%	$166.15	$166.15	$166.15	$166.20
Purchase #2	$100.83	10.251%	$111.1661	$111.17	$111.15	$111.20
Purchase #3	$187.40	3.525%	$194.0059	$194.01	$194.00	$194.00
Purchase #4	$58.28	8.323%	$63.1306	$63.13	$63.15	$63.10
Purchase #5	$42.70	12.733%	$48.137	$48.14	$48.15	$48.10
Purchase #6	$179.43	7.758%	$193.3502	$193.35	$193.35	$193.40
Purchase #7	$37.89	13.321%	$42.9373	$42.94	$42.95	$42.90
7 purchase totals =	$757.08		$818.8771	$818.89	$818.90	$818.90