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	$21.73	10.165%	$23.9389	$23.94	$23.95	$23.90
Purchase #2	$233.48	12.383%	$262.3918	$262.39	$262.40	$262.40
Purchase #3	$26.33	4.759%	$27.583	$27.58	$27.60	$27.60
Purchase #4	$82.36	8.565%	$89.4141	$89.41	$89.40	$89.40
Purchase #5	$57.74	12.554%	$64.9887	$64.99	$65.00	$65.00
Purchase #6	$53.66	11.476%	$59.818	$59.82	$59.80	$59.80
Purchase #7	$95.41	8.131%	$103.1678	$103.17	$103.15	$103.20
7 purchase totals =	$570.71		$631.3023	$631.30	$631.30	$631.30