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	$39.51	10.588%	$43.6933	$43.69	$43.70	$43.70
Purchase #2	$17.96	13.685%	$20.4178	$20.42	$20.40	$20.40
Purchase #3	$160.37	4.295%	$167.2579	$167.26	$167.25	$167.30
Purchase #4	$56.52	4.624%	$59.1335	$59.13	$59.15	$59.10
Purchase #5	$48.68	5.804%	$51.5054	$51.51	$51.50	$51.50
Purchase #6	$247.59	9.297%	$270.6084	$270.61	$270.60	$270.60
Purchase #7	$14.84	9.598%	$16.2643	$16.26	$16.25	$16.30
7 purchase totals =	$585.47		$628.8806	$628.88	$628.85	$628.90