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	$159.69	11.802%	$178.5366	$178.54	$178.55	$178.50
Purchase #2	$151.29	13.870%	$172.2739	$172.27	$172.25	$172.30
Purchase #3	$49.25	10.338%	$54.3415	$54.34	$54.35	$54.30
Purchase #4	$29.73	5.511%	$31.3684	$31.37	$31.35	$31.40
Purchase #5	$16.87	4.312%	$17.5974	$17.60	$17.60	$17.60
Purchase #6	$183.87	3.301%	$189.9395	$189.94	$189.95	$189.90
Purchase #7	$175.99	11.502%	$196.2324	$196.23	$196.25	$196.20
7 purchase totals =	$766.69		$840.2897	$840.29	$840.30	$840.20