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	$32.60	11.278%	$36.2766	$36.28	$36.30	$36.30
Purchase #2	$132.50	9.224%	$144.7218	$144.72	$144.70	$144.70
Purchase #3	$142.62	13.603%	$162.0206	$162.02	$162.00	$162.00
Purchase #4	$98.90	12.720%	$111.4801	$111.48	$111.50	$111.50
Purchase #5	$46.43	8.604%	$50.4248	$50.42	$50.40	$50.40
Purchase #6	$97.40	12.503%	$109.5779	$109.58	$109.60	$109.60
Purchase #7	$118.79	4.744%	$124.4254	$124.43	$124.45	$124.40
7 purchase totals =	$669.24		$738.9272	$738.93	$738.95	$738.90