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	$74.98	10.660%	$82.9729	$82.97	$82.95	$83.00
Purchase #2	$139.39	12.837%	$157.2835	$157.28	$157.30	$157.30
Purchase #3	$98.91	12.708%	$111.4795	$111.48	$111.50	$111.50
Purchase #4	$166.70	10.452%	$184.1235	$184.12	$184.10	$184.10
Purchase #5	$233.74	9.857%	$256.7798	$256.78	$256.80	$256.80
Purchase #6	$98.61	10.149%	$108.6179	$108.62	$108.60	$108.60
Purchase #7	$80.39	4.133%	$83.7125	$83.71	$83.70	$83.70
7 purchase totals =	$892.72		$984.9696	$984.96	$984.95	$985.00