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	$238.59	12.509%	$268.4352	$268.44	$268.45	$268.40
Purchase #2	$29.89	11.567%	$33.3474	$33.35	$33.35	$33.30
Purchase #3	$33.33	11.830%	$37.2729	$37.27	$37.25	$37.30
Purchase #4	$102.41	5.129%	$107.6626	$107.66	$107.65	$107.70
Purchase #5	$97.56	7.693%	$105.0653	$105.07	$105.05	$105.10
Purchase #6	$52.84	10.690%	$58.4886	$58.49	$58.50	$58.50
Purchase #7	$33.41	13.391%	$37.8839	$37.88	$37.90	$37.90
7 purchase totals =	$588.03		$648.1559	$648.16	$648.15	$648.20