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	$214.78	13.700%	$244.2049	$244.20	$244.20	$244.20
Purchase #2	$107.75	3.382%	$111.3941	$111.39	$111.40	$111.40
Purchase #3	$238.31	12.711%	$268.6016	$268.60	$268.60	$268.60
Purchase #4	$20.69	3.494%	$21.4129	$21.41	$21.40	$21.40
Purchase #5	$50.55	5.472%	$53.3161	$53.32	$53.30	$53.30
Purchase #6	$10.72	3.505%	$11.0957	$11.10	$11.10	$11.10
Purchase #7	$214.78	6.747%	$229.2712	$229.27	$229.25	$229.30
7 purchase totals =	$857.58		$939.2965	$939.29	$939.25	$939.30