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	$91.60	12.593%	$103.1352	$103.14	$103.15	$103.10
Purchase #2	$118.93	13.131%	$134.5467	$134.55	$134.55	$134.50
Purchase #3	$247.40	7.338%	$265.5542	$265.55	$265.55	$265.60
Purchase #4	$245.47	11.761%	$274.3397	$274.34	$274.35	$274.30
Purchase #5	$112.37	10.261%	$123.9003	$123.90	$123.90	$123.90
Purchase #6	$99.95	6.525%	$106.4717	$106.47	$106.45	$106.50
Purchase #7	$59.52	6.439%	$63.3525	$63.35	$63.35	$63.40
7 purchase totals =	$975.24		$1,071.3003	$1,071.30	$1,071.30	$1,071.30