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	$165.60	10.806%	$183.4947	$183.49	$183.50	$183.50
Purchase #2	$158.79	7.748%	$171.093	$171.09	$171.10	$171.10
Purchase #3	$123.50	6.546%	$131.5843	$131.58	$131.60	$131.60
Purchase #4	$133.36	8.592%	$144.8183	$144.82	$144.80	$144.80
Purchase #5	$243.70	11.727%	$272.2787	$272.28	$272.30	$272.30
Purchase #6	$153.28	13.846%	$174.5031	$174.50	$174.50	$174.50
Purchase #7	$131.93	5.250%	$138.8563	$138.86	$138.85	$138.90
7 purchase totals =	$1,110.16		$1,216.6284	$1,216.62	$1,216.65	$1,216.70