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	$21.96	10.734%	$24.3172	$24.32	$24.30	$24.30
Purchase #2	$100.52	6.590%	$107.1443	$107.14	$107.15	$107.10
Purchase #3	$54.73	5.357%	$57.6619	$57.66	$57.65	$57.70
Purchase #4	$195.73	13.519%	$222.1907	$222.19	$222.20	$222.20
Purchase #5	$142.40	10.543%	$157.4132	$157.41	$157.40	$157.40
Purchase #6	$160.98	7.129%	$172.4563	$172.46	$172.45	$172.50
Purchase #7	$81.95	9.646%	$89.8549	$89.85	$89.85	$89.90
7 purchase totals =	$758.27		$831.0385	$831.03	$831.00	$831.10