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	$49.73	13.436%	$56.4117	$56.41	$56.40	$56.40
Purchase #2	$103.29	3.461%	$106.8649	$106.86	$106.85	$106.90
Purchase #3	$44.72	6.240%	$47.5105	$47.51	$47.50	$47.50
Purchase #4	$99.47	3.768%	$103.218	$103.22	$103.20	$103.20
Purchase #5	$77.85	9.784%	$85.4668	$85.47	$85.45	$85.50
Purchase #6	$103.34	11.419%	$115.1404	$115.14	$115.15	$115.10
Purchase #7	$19.54	11.240%	$21.7363	$21.74	$21.75	$21.70
7 purchase totals =	$497.94		$536.3486	$536.35	$536.30	$536.30