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	$92.58	11.805%	$103.5091	$103.51	$103.50	$103.50
Purchase #2	$244.74	6.771%	$261.3113	$261.31	$261.30	$261.30
Purchase #3	$38.60	11.467%	$43.0263	$43.03	$43.05	$43.00
Purchase #4	$218.83	12.714%	$246.652	$246.65	$246.65	$246.70
Purchase #5	$61.82	7.120%	$66.2216	$66.22	$66.20	$66.20
Purchase #6	$83.72	8.558%	$90.8848	$90.88	$90.90	$90.90
Purchase #7	$103.91	13.397%	$117.8308	$117.83	$117.85	$117.80
7 purchase totals =	$844.20		$929.4359	$929.43	$929.45	$929.40