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	$40.38	5.636%	$42.6558	$42.66	$42.65	$42.70
Purchase #2	$139.65	4.416%	$145.8169	$145.82	$145.80	$145.80
Purchase #3	$9.57	13.508%	$10.8627	$10.86	$10.85	$10.90
Purchase #4	$242.57	9.409%	$265.3934	$265.39	$265.40	$265.40
Purchase #5	$80.58	3.434%	$83.3471	$83.35	$83.35	$83.30
Purchase #6	$22.26	12.158%	$24.9664	$24.97	$24.95	$25.00
Purchase #7	$52.47	4.279%	$54.7152	$54.72	$54.70	$54.70
7 purchase totals =	$587.48		$627.7575	$627.77	$627.70	$627.80