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	$26.81	8.813%	$29.1728	$29.17	$29.15	$29.20
Purchase #2	$59.41	4.666%	$62.1821	$62.18	$62.20	$62.20
Purchase #3	$126.61	11.426%	$141.0765	$141.08	$141.10	$141.10
Purchase #4	$207.97	12.670%	$234.3198	$234.32	$234.30	$234.30
Purchase #5	$103.91	12.395%	$116.7896	$116.79	$116.80	$116.80
Purchase #6	$98.50	12.816%	$111.1238	$111.12	$111.10	$111.10
Purchase #7	$224.68	4.117%	$233.9301	$233.93	$233.95	$233.90
7 purchase totals =	$847.89		$928.5947	$928.59	$928.60	$928.60