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	$164.88	9.381%	$180.3474	$180.35	$180.35	$180.30
Purchase #2	$99.92	4.502%	$104.4184	$104.42	$104.40	$104.40
Purchase #3	$158.66	5.527%	$167.4291	$167.43	$167.45	$167.40
Purchase #4	$12.65	13.227%	$14.3232	$14.32	$14.30	$14.30
Purchase #5	$87.53	3.490%	$90.5848	$90.58	$90.60	$90.60
Purchase #6	$90.82	11.617%	$101.3706	$101.37	$101.35	$101.40
Purchase #7	$83.43	9.331%	$91.2149	$91.21	$91.20	$91.20
7 purchase totals =	$697.89		$749.6884	$749.68	$749.65	$749.60