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	$43.86	12.445%	$49.3184	$49.32	$49.30	$49.30
Purchase #2	$159.25	13.154%	$180.1977	$180.20	$180.20	$180.20
Purchase #3	$77.78	5.671%	$82.1909	$82.19	$82.20	$82.20
Purchase #4	$117.29	11.202%	$130.4288	$130.43	$130.45	$130.40
Purchase #5	$172.77	13.606%	$196.2771	$196.28	$196.30	$196.30
Purchase #6	$164.37	8.764%	$178.7754	$178.78	$178.80	$178.80
Purchase #7	$245.41	10.274%	$270.6234	$270.62	$270.60	$270.60
7 purchase totals =	$980.73		$1,087.8117	$1,087.82	$1,087.85	$1,087.80