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	$167.44	13.733%	$190.4345	$190.43	$190.45	$190.40
Purchase #2	$101.58	7.450%	$109.1477	$109.15	$109.15	$109.10
Purchase #3	$186.54	11.678%	$208.3241	$208.32	$208.30	$208.30
Purchase #4	$242.93	5.209%	$255.5842	$255.58	$255.60	$255.60
Purchase #5	$130.83	7.589%	$140.7587	$140.76	$140.75	$140.80
Purchase #6	$136.87	5.331%	$144.1665	$144.17	$144.15	$144.20
Purchase #7	$248.51	12.462%	$279.4793	$279.48	$279.50	$279.50
7 purchase totals =	$1,214.70		$1,327.8950	$1,327.89	$1,327.90	$1,327.90