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	$45.55	3.526%	$47.1561	$47.16	$47.15	$47.20
Purchase #2	$133.64	9.528%	$146.3732	$146.37	$146.35	$146.40
Purchase #3	$193.76	11.434%	$215.9145	$215.91	$215.90	$215.90
Purchase #4	$10.72	10.159%	$11.809	$11.81	$11.80	$11.80
Purchase #5	$112.85	5.329%	$118.8638	$118.86	$118.85	$118.90
Purchase #6	$84.44	6.593%	$90.0071	$90.01	$90.00	$90.00
Purchase #7	$150.87	4.711%	$157.9775	$157.98	$158.00	$158.00
7 purchase totals =	$731.83		$788.1012	$788.10	$788.05	$788.20