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	$166.71	8.733%	$181.2688	$181.27	$181.25	$181.30
Purchase #2	$167.87	11.104%	$186.5103	$186.51	$186.50	$186.50
Purchase #3	$189.84	7.408%	$203.9033	$203.90	$203.90	$203.90
Purchase #4	$240.64	6.191%	$255.538	$255.54	$255.55	$255.50
Purchase #5	$174.47	7.247%	$187.1138	$187.11	$187.10	$187.10
Purchase #6	$40.94	13.819%	$46.5975	$46.60	$46.60	$46.60
Purchase #7	$242.74	13.242%	$274.8836	$274.88	$274.90	$274.90
7 purchase totals =	$1,223.21		$1,335.8153	$1,335.81	$1,335.80	$1,335.80