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	$18.31	13.262%	$20.7383	$20.74	$20.75	$20.70
Purchase #2	$44.36	8.521%	$48.1399	$48.14	$48.15	$48.10
Purchase #3	$98.72	5.278%	$103.9304	$103.93	$103.95	$103.90
Purchase #4	$132.75	11.784%	$148.3933	$148.39	$148.40	$148.40
Purchase #5	$17.37	8.297%	$18.8112	$18.81	$18.80	$18.80
Purchase #6	$53.51	4.373%	$55.85	$55.85	$55.85	$55.90
Purchase #7	$213.33	6.437%	$227.0621	$227.06	$227.05	$227.10
7 purchase totals =	$578.35		$622.9252	$622.92	$622.95	$622.90