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	$170.66	6.536%	$181.8143	$181.81	$181.80	$181.80
Purchase #2	$228.83	12.698%	$257.8868	$257.89	$257.90	$257.90
Purchase #3	$52.45	5.423%	$55.2944	$55.29	$55.30	$55.30
Purchase #4	$78.40	4.786%	$82.1522	$82.15	$82.15	$82.20
Purchase #5	$173.28	7.816%	$186.8236	$186.82	$186.80	$186.80
Purchase #6	$200.59	9.624%	$219.8948	$219.89	$219.90	$219.90
Purchase #7	$137.38	5.603%	$145.0774	$145.08	$145.10	$145.10
7 purchase totals =	$1,041.59		$1,128.9435	$1,128.93	$1,128.95	$1,129.00