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	$29.81	4.104%	$31.0334	$31.03	$31.05	$31.00
Purchase #2	$71.86	6.376%	$76.4418	$76.44	$76.45	$76.40
Purchase #3	$72.52	5.267%	$76.3396	$76.34	$76.35	$76.30
Purchase #4	$17.84	5.456%	$18.8134	$18.81	$18.80	$18.80
Purchase #5	$65.28	10.321%	$72.0175	$72.02	$72.00	$72.00
Purchase #6	$249.44	3.599%	$258.4173	$258.42	$258.40	$258.40
Purchase #7	$143.39	13.588%	$162.8738	$162.87	$162.85	$162.90
7 purchase totals =	$650.14		$695.9368	$695.93	$695.90	$695.80