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	$162.67	12.819%	$183.5227	$183.52	$183.50	$183.50
Purchase #2	$250.65	11.653%	$279.8582	$279.86	$279.85	$279.90
Purchase #3	$243.31	5.754%	$257.3101	$257.31	$257.30	$257.30
Purchase #4	$96.97	12.577%	$109.1659	$109.17	$109.15	$109.20
Purchase #5	$153.59	13.168%	$173.8147	$173.81	$173.80	$173.80
Purchase #6	$85.72	5.308%	$90.27	$90.27	$90.25	$90.30
Purchase #7	$191.80	3.826%	$199.1383	$199.14	$199.15	$199.10
7 purchase totals =	$1,184.71		$1,293.0799	$1,293.08	$1,293.00	$1,293.10