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	$171.85	5.321%	$180.9941	$180.99	$181.00	$181.00
Purchase #2	$183.39	9.381%	$200.5938	$200.59	$200.60	$200.60
Purchase #3	$112.70	13.254%	$127.6373	$127.64	$127.65	$127.60
Purchase #4	$105.56	10.575%	$116.723	$116.72	$116.70	$116.70
Purchase #5	$94.52	11.780%	$105.6545	$105.65	$105.65	$105.70
Purchase #6	$11.29	8.516%	$12.2515	$12.25	$12.25	$12.30
Purchase #7	$112.79	10.383%	$124.501	$124.50	$124.50	$124.50
7 purchase totals =	$792.10		$868.3552	$868.34	$868.35	$868.40