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	$86.34	5.129%	$90.7684	$90.77	$90.75	$90.80
Purchase #2	$128.43	11.580%	$143.3022	$143.30	$143.30	$143.30
Purchase #3	$15.69	10.784%	$17.382	$17.38	$17.40	$17.40
Purchase #4	$226.28	12.175%	$253.8296	$253.83	$253.85	$253.80
Purchase #5	$38.94	3.769%	$40.4076	$40.41	$40.40	$40.40
Purchase #6	$172.67	8.301%	$187.0033	$187.00	$187.00	$187.00
Purchase #7	$159.58	11.742%	$178.3179	$178.32	$178.30	$178.30
7 purchase totals =	$827.93		$911.0110	$911.01	$911.00	$911.00