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	$15.44	7.479%	$16.5948	$16.59	$16.60	$16.60
Purchase #2	$156.37	7.333%	$167.8366	$167.84	$167.85	$167.80
Purchase #3	$156.60	9.298%	$171.1607	$171.16	$171.15	$171.20
Purchase #4	$99.51	11.848%	$111.2999	$111.30	$111.30	$111.30
Purchase #5	$40.32	8.649%	$43.8073	$43.81	$43.80	$43.80
Purchase #6	$21.48	12.334%	$24.1293	$24.13	$24.15	$24.10
Purchase #7	$169.66	10.726%	$187.8577	$187.86	$187.85	$187.90
7 purchase totals =	$659.38		$722.6863	$722.69	$722.70	$722.70