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	$12.32	3.209%	$12.7153	$12.72	$12.70	$12.70
Purchase #2	$120.72	5.467%	$127.3198	$127.32	$127.30	$127.30
Purchase #3	$147.28	3.739%	$152.7868	$152.79	$152.80	$152.80
Purchase #4	$172.57	8.830%	$187.8079	$187.81	$187.80	$187.80
Purchase #5	$161.28	6.772%	$172.2019	$172.20	$172.20	$172.20
Purchase #6	$162.78	10.624%	$180.0737	$180.07	$180.05	$180.10
Purchase #7	$61.44	6.341%	$65.3359	$65.34	$65.35	$65.30
7 purchase totals =	$838.39		$898.2413	$898.25	$898.20	$898.20