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	$123.41	11.414%	$137.496	$137.50	$137.50	$137.50
Purchase #2	$35.28	8.568%	$38.3028	$38.30	$38.30	$38.30
Purchase #3	$74.44	9.204%	$81.2915	$81.29	$81.30	$81.30
Purchase #4	$93.38	10.478%	$103.1644	$103.16	$103.15	$103.20
Purchase #5	$226.41	3.482%	$234.2936	$234.29	$234.30	$234.30
Purchase #6	$56.77	8.276%	$61.4683	$61.47	$61.45	$61.50
Purchase #7	$164.58	12.448%	$185.0669	$185.07	$185.05	$185.10
7 purchase totals =	$774.27		$841.0835	$841.08	$841.05	$841.20