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	$159.78	12.198%	$179.27	$179.27	$179.25	$179.30
Purchase #2	$138.44	10.713%	$153.2711	$153.27	$153.25	$153.30
Purchase #3	$51.27	10.471%	$56.6385	$56.64	$56.65	$56.60
Purchase #4	$82.29	8.481%	$89.269	$89.27	$89.25	$89.30
Purchase #5	$176.36	9.847%	$193.7262	$193.73	$193.75	$193.70
Purchase #6	$203.45	11.672%	$227.1967	$227.20	$227.20	$227.20
Purchase #7	$159.87	4.788%	$167.5246	$167.52	$167.50	$167.50
7 purchase totals =	$971.46		$1,066.8961	$1,066.90	$1,066.85	$1,066.90