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	$103.69	5.499%	$109.3919	$109.39	$109.40	$109.40
Purchase #2	$98.59	5.727%	$104.2362	$104.24	$104.25	$104.20
Purchase #3	$129.57	12.571%	$145.8582	$145.86	$145.85	$145.90
Purchase #4	$135.65	9.675%	$148.7741	$148.77	$148.75	$148.80
Purchase #5	$103.93	3.806%	$107.8856	$107.89	$107.90	$107.90
Purchase #6	$223.33	12.147%	$250.4579	$250.46	$250.45	$250.50
Purchase #7	$244.28	4.827%	$256.0714	$256.07	$256.05	$256.10
7 purchase totals =	$1,039.04		$1,122.6753	$1,122.68	$1,122.65	$1,122.80