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	$137.56	3.791%	$142.7749	$142.77	$142.75	$142.80
Purchase #2	$134.70	8.459%	$146.0943	$146.09	$146.10	$146.10
Purchase #3	$224.63	7.376%	$241.1987	$241.20	$241.20	$241.20
Purchase #4	$35.44	5.125%	$37.2563	$37.26	$37.25	$37.30
Purchase #5	$99.49	12.171%	$111.5989	$111.60	$111.60	$111.60
Purchase #6	$86.60	4.420%	$90.4277	$90.43	$90.45	$90.40
Purchase #7	$163.63	5.822%	$173.1565	$173.16	$173.15	$173.20
7 purchase totals =	$882.05		$942.5073	$942.51	$942.50	$942.60