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	$158.98	9.389%	$173.9066	$173.91	$173.90	$173.90
Purchase #2	$36.64	9.569%	$40.1461	$40.15	$40.15	$40.10
Purchase #3	$113.57	9.666%	$124.5477	$124.55	$124.55	$124.50
Purchase #4	$38.74	13.169%	$43.8417	$43.84	$43.85	$43.80
Purchase #5	$110.65	5.289%	$116.5023	$116.50	$116.50	$116.50
Purchase #6	$79.81	8.371%	$86.4909	$86.49	$86.50	$86.50
Purchase #7	$32.93	13.242%	$37.2906	$37.29	$37.30	$37.30
7 purchase totals =	$571.32		$622.7259	$622.73	$622.75	$622.60