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	$146.82	12.314%	$164.8994	$164.90	$164.90	$164.90
Purchase #2	$145.27	10.501%	$160.5248	$160.52	$160.50	$160.50
Purchase #3	$56.59	10.605%	$62.5914	$62.59	$62.60	$62.60
Purchase #4	$245.99	5.180%	$258.7323	$258.73	$258.75	$258.70
Purchase #5	$10.32	11.771%	$11.5348	$11.53	$11.55	$11.50
Purchase #6	$91.80	7.295%	$98.4968	$98.50	$98.50	$98.50
Purchase #7	$27.74	6.385%	$29.5112	$29.51	$29.50	$29.50
7 purchase totals =	$724.53		$786.2907	$786.28	$786.30	$786.20