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	$111.65	10.189%	$123.026	$123.03	$123.05	$123.00
Purchase #2	$103.71	7.202%	$111.1792	$111.18	$111.20	$111.20
Purchase #3	$133.82	10.186%	$147.4509	$147.45	$147.45	$147.50
Purchase #4	$33.45	9.218%	$36.5334	$36.53	$36.55	$36.50
Purchase #5	$224.82	9.334%	$245.8047	$245.80	$245.80	$245.80
Purchase #6	$90.74	9.362%	$99.2351	$99.24	$99.25	$99.20
Purchase #7	$67.72	3.111%	$69.8268	$69.83	$69.85	$69.80
7 purchase totals =	$765.91		$833.0561	$833.06	$833.15	$833.00