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	$33.52	12.572%	$37.7341	$37.73	$37.75	$37.70
Purchase #2	$70.98	13.459%	$80.5332	$80.53	$80.55	$80.50
Purchase #3	$181.85	10.187%	$200.3751	$200.38	$200.40	$200.40
Purchase #4	$125.57	7.643%	$135.1673	$135.17	$135.15	$135.20
Purchase #5	$27.99	5.461%	$29.5185	$29.52	$29.50	$29.50
Purchase #6	$54.40	13.251%	$61.6085	$61.61	$61.60	$61.60
Purchase #7	$158.43	9.142%	$172.9137	$172.91	$172.90	$172.90
7 purchase totals =	$652.74		$717.8504	$717.85	$717.85	$717.80