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	$34.28	5.830%	$36.2785	$36.28	$36.30	$36.30
Purchase #2	$164.82	10.598%	$182.2876	$182.29	$182.30	$182.30
Purchase #3	$99.83	5.554%	$105.3746	$105.37	$105.35	$105.40
Purchase #4	$68.98	4.843%	$72.3207	$72.32	$72.30	$72.30
Purchase #5	$143.54	5.791%	$151.8524	$151.85	$151.85	$151.90
Purchase #6	$85.97	6.533%	$91.5864	$91.59	$91.60	$91.60
Purchase #7	$155.82	10.499%	$172.1795	$172.18	$172.20	$172.20
7 purchase totals =	$753.24		$811.8797	$811.88	$811.90	$812.00