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	$39.75	13.161%	$44.9815	$44.98	$45.00	$45.00
Purchase #2	$101.60	9.517%	$111.2693	$111.27	$111.25	$111.30
Purchase #3	$49.47	12.297%	$55.5533	$55.55	$55.55	$55.60
Purchase #4	$172.60	5.207%	$181.5873	$181.59	$181.60	$181.60
Purchase #5	$145.42	6.329%	$154.6236	$154.62	$154.60	$154.60
Purchase #6	$119.82	5.507%	$126.4185	$126.42	$126.40	$126.40
Purchase #7	$231.90	9.705%	$254.4059	$254.41	$254.40	$254.40
7 purchase totals =	$860.56		$928.8394	$928.84	$928.80	$928.90