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	$113.91	12.273%	$127.8902	$127.89	$127.90	$127.90
Purchase #2	$61.74	5.149%	$64.919	$64.92	$64.90	$64.90
Purchase #3	$219.40	7.120%	$235.0213	$235.02	$235.00	$235.00
Purchase #4	$58.73	13.585%	$66.7085	$66.71	$66.70	$66.70
Purchase #5	$10.86	9.367%	$11.8773	$11.88	$11.90	$11.90
Purchase #6	$52.31	3.712%	$54.2517	$54.25	$54.25	$54.30
Purchase #7	$18.91	9.721%	$20.7482	$20.75	$20.75	$20.70
7 purchase totals =	$535.86		$581.4162	$581.42	$581.40	$581.40