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	$17.71	6.637%	$18.8854	$18.89	$18.90	$18.90
Purchase #2	$100.78	13.715%	$114.602	$114.60	$114.60	$114.60
Purchase #3	$233.47	12.680%	$263.074	$263.07	$263.05	$263.10
Purchase #4	$250.37	8.800%	$272.4026	$272.40	$272.40	$272.40
Purchase #5	$94.51	9.544%	$103.53	$103.53	$103.55	$103.50
Purchase #6	$183.65	11.772%	$205.2693	$205.27	$205.25	$205.30
Purchase #7	$14.75	4.492%	$15.4126	$15.41	$15.40	$15.40
7 purchase totals =	$895.24		$993.1759	$993.17	$993.15	$993.20