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	$45.43	10.155%	$50.0434	$50.04	$50.05	$50.00
Purchase #2	$11.83	10.225%	$13.0396	$13.04	$13.05	$13.00
Purchase #3	$98.65	7.341%	$105.8919	$105.89	$105.90	$105.90
Purchase #4	$215.97	3.150%	$222.7731	$222.77	$222.75	$222.80
Purchase #5	$228.85	10.383%	$252.6115	$252.61	$252.60	$252.60
Purchase #6	$77.41	12.464%	$87.0584	$87.06	$87.05	$87.10
Purchase #7	$6.51	5.455%	$6.8651	$6.87	$6.85	$6.90
7 purchase totals =	$684.65		$738.2830	$738.28	$738.25	$738.30