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	$113.60	13.305%	$128.7145	$128.71	$128.70	$128.70
Purchase #2	$135.77	12.460%	$152.6869	$152.69	$152.70	$152.70
Purchase #3	$34.99	13.209%	$39.6118	$39.61	$39.60	$39.60
Purchase #4	$88.83	8.113%	$96.0368	$96.04	$96.05	$96.00
Purchase #5	$190.51	3.341%	$196.8749	$196.87	$196.85	$196.90
Purchase #6	$40.30	9.628%	$44.1801	$44.18	$44.20	$44.20
Purchase #7	$30.48	5.864%	$32.2673	$32.27	$32.25	$32.30
7 purchase totals =	$634.48		$690.3723	$690.37	$690.35	$690.40