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	$85.88	13.751%	$97.6894	$97.69	$97.70	$97.70
Purchase #2	$108.79	3.538%	$112.639	$112.64	$112.65	$112.60
Purchase #3	$69.72	12.122%	$78.1715	$78.17	$78.15	$78.20
Purchase #4	$152.50	13.195%	$172.6224	$172.62	$172.60	$172.60
Purchase #5	$242.67	4.369%	$253.2723	$253.27	$253.25	$253.30
Purchase #6	$117.59	3.827%	$122.0902	$122.09	$122.10	$122.10
Purchase #7	$19.98	4.468%	$20.8727	$20.87	$20.85	$20.90
7 purchase totals =	$797.13		$857.3575	$857.35	$857.30	$857.40