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	$250.46	11.618%	$279.5584	$279.56	$279.55	$279.60
Purchase #2	$76.32	8.243%	$82.6111	$82.61	$82.60	$82.60
Purchase #3	$14.82	5.836%	$15.6849	$15.68	$15.70	$15.70
Purchase #4	$96.29	7.525%	$103.5358	$103.54	$103.55	$103.50
Purchase #5	$41.42	10.251%	$45.666	$45.67	$45.65	$45.70
Purchase #6	$75.34	6.747%	$80.4232	$80.42	$80.40	$80.40
Purchase #7	$29.31	6.548%	$31.2292	$31.23	$31.25	$31.20
7 purchase totals =	$583.96		$638.7086	$638.71	$638.70	$638.70