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	$141.57	8.274%	$153.2835	$153.28	$153.30	$153.30
Purchase #2	$77.64	13.531%	$88.1455	$88.15	$88.15	$88.10
Purchase #3	$71.89	7.667%	$77.4018	$77.40	$77.40	$77.40
Purchase #4	$90.38	4.793%	$94.7119	$94.71	$94.70	$94.70
Purchase #5	$125.38	5.725%	$132.558	$132.56	$132.55	$132.60
Purchase #6	$218.71	5.339%	$230.3869	$230.39	$230.40	$230.40
Purchase #7	$50.74	7.406%	$54.4978	$54.50	$54.50	$54.50
7 purchase totals =	$776.31		$830.9854	$830.99	$831.00	$831.00