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	$151.34	9.412%	$165.5841	$165.58	$165.60	$165.60
Purchase #2	$227.63	13.516%	$258.3965	$258.40	$258.40	$258.40
Purchase #3	$118.85	4.773%	$124.5227	$124.52	$124.50	$124.50
Purchase #4	$80.39	3.585%	$83.272	$83.27	$83.25	$83.30
Purchase #5	$142.92	12.128%	$160.2533	$160.25	$160.25	$160.30
Purchase #6	$17.38	10.217%	$19.1557	$19.16	$19.15	$19.20
Purchase #7	$33.46	4.274%	$34.8901	$34.89	$34.90	$34.90
7 purchase totals =	$771.97		$846.0744	$846.07	$846.05	$846.20