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	$12.90	7.153%	$13.8227	$13.82	$13.80	$13.80
Purchase #2	$53.59	10.231%	$59.0728	$59.07	$59.05	$59.10
Purchase #3	$14.45	4.851%	$15.151	$15.15	$15.15	$15.20
Purchase #4	$57.45	13.160%	$65.0104	$65.01	$65.00	$65.00
Purchase #5	$68.91	12.418%	$77.4672	$77.47	$77.45	$77.50
Purchase #6	$139.83	6.568%	$149.014	$149.01	$149.00	$149.00
Purchase #7	$138.75	11.768%	$155.0781	$155.08	$155.10	$155.10
7 purchase totals =	$485.88		$534.6162	$534.61	$534.55	$534.70