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	$63.84	6.624%	$68.0688	$68.07	$68.05	$68.10
Purchase #2	$162.69	9.672%	$178.4254	$178.43	$178.45	$178.40
Purchase #3	$35.60	8.320%	$38.5619	$38.56	$38.55	$38.60
Purchase #4	$35.65	4.838%	$37.3747	$37.37	$37.35	$37.40
Purchase #5	$239.35	10.158%	$263.6632	$263.66	$263.65	$263.70
Purchase #6	$162.70	10.460%	$179.7184	$179.72	$179.70	$179.70
Purchase #7	$103.47	7.389%	$111.1154	$111.12	$111.10	$111.10
7 purchase totals =	$803.30		$876.9278	$876.93	$876.85	$877.00