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	$154.59	10.666%	$171.0786	$171.08	$171.10	$171.10
Purchase #2	$34.97	11.416%	$38.9622	$38.96	$38.95	$39.00
Purchase #3	$66.32	7.868%	$71.5381	$71.54	$71.55	$71.50
Purchase #4	$30.47	9.847%	$33.4704	$33.47	$33.45	$33.50
Purchase #5	$92.49	12.247%	$103.8173	$103.82	$103.80	$103.80
Purchase #6	$116.73	7.268%	$125.2139	$125.21	$125.20	$125.20
Purchase #7	$235.70	8.412%	$255.5271	$255.53	$255.55	$255.50
7 purchase totals =	$731.27		$799.6076	$799.61	$799.60	$799.60