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	$90.78	11.773%	$101.4675	$101.47	$101.45	$101.50
Purchase #2	$40.40	5.158%	$42.4838	$42.48	$42.50	$42.50
Purchase #3	$118.30	8.834%	$128.7506	$128.75	$128.75	$128.80
Purchase #4	$75.68	3.657%	$78.4476	$78.45	$78.45	$78.40
Purchase #5	$120.94	6.483%	$128.7805	$128.78	$128.80	$128.80
Purchase #6	$88.56	7.384%	$95.0993	$95.10	$95.10	$95.10
Purchase #7	$16.71	6.790%	$17.8446	$17.84	$17.85	$17.80
7 purchase totals =	$551.37		$592.8739	$592.87	$592.90	$592.90