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	$173.83	4.298%	$181.3012	$181.30	$181.30	$181.30
Purchase #2	$54.63	7.196%	$58.5612	$58.56	$58.55	$58.60
Purchase #3	$27.90	4.239%	$29.0827	$29.08	$29.10	$29.10
Purchase #4	$49.93	13.200%	$56.5208	$56.52	$56.50	$56.50
Purchase #5	$33.32	13.464%	$37.8062	$37.81	$37.80	$37.80
Purchase #6	$151.86	11.274%	$168.9807	$168.98	$169.00	$169.00
Purchase #7	$235.97	5.109%	$248.0257	$248.03	$248.05	$248.00
7 purchase totals =	$727.44		$780.2785	$780.28	$780.30	$780.30