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	$144.49	13.577%	$164.1074	$164.11	$164.10	$164.10
Purchase #2	$167.97	7.163%	$180.0017	$180.00	$180.00	$180.00
Purchase #3	$81.38	10.286%	$89.7507	$89.75	$89.75	$89.80
Purchase #4	$72.53	9.855%	$79.6778	$79.68	$79.70	$79.70
Purchase #5	$46.78	7.845%	$50.4499	$50.45	$50.45	$50.40
Purchase #6	$117.66	4.604%	$123.0771	$123.08	$123.10	$123.10
Purchase #7	$54.49	12.823%	$61.4773	$61.48	$61.50	$61.50
7 purchase totals =	$685.30		$748.5419	$748.55	$748.60	$748.60