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	$247.75	8.390%	$268.5362	$268.54	$268.55	$268.50
Purchase #2	$205.66	10.294%	$226.8306	$226.83	$226.85	$226.80
Purchase #3	$127.70	9.736%	$140.1329	$140.13	$140.15	$140.10
Purchase #4	$216.87	7.616%	$233.3868	$233.39	$233.40	$233.40
Purchase #5	$100.71	10.758%	$111.5444	$111.54	$111.55	$111.50
Purchase #6	$142.86	12.619%	$160.8875	$160.89	$160.90	$160.90
Purchase #7	$179.61	13.717%	$204.2471	$204.25	$204.25	$204.20
7 purchase totals =	$1,221.16		$1,345.5655	$1,345.57	$1,345.65	$1,345.40