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	$37.42	13.448%	$42.4522	$42.45	$42.45	$42.50
Purchase #2	$125.30	6.593%	$133.561	$133.56	$133.55	$133.60
Purchase #3	$166.83	12.254%	$187.2733	$187.27	$187.25	$187.30
Purchase #4	$139.29	4.741%	$145.8937	$145.89	$145.90	$145.90
Purchase #5	$102.82	8.186%	$111.2368	$111.24	$111.25	$111.20
Purchase #6	$107.92	3.645%	$111.8537	$111.85	$111.85	$111.90
Purchase #7	$92.58	9.404%	$101.2862	$101.29	$101.30	$101.30
7 purchase totals =	$772.16		$833.5569	$833.55	$833.55	$833.70