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	$13.48	12.288%	$15.1364	$15.14	$15.15	$15.10
Purchase #2	$201.59	13.104%	$228.0064	$228.01	$228.00	$228.00
Purchase #3	$187.63	9.674%	$205.7813	$205.78	$205.80	$205.80
Purchase #4	$240.48	8.152%	$260.0839	$260.08	$260.10	$260.10
Purchase #5	$95.55	4.249%	$99.6099	$99.61	$99.60	$99.60
Purchase #6	$158.38	9.167%	$172.8987	$172.90	$172.90	$172.90
Purchase #7	$113.36	4.370%	$118.3138	$118.31	$118.30	$118.30
7 purchase totals =	$1,010.47		$1,099.8304	$1,099.83	$1,099.85	$1,099.80