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	$249.34	9.213%	$272.3117	$272.31	$272.30	$272.30
Purchase #2	$9.29	12.635%	$10.4638	$10.46	$10.45	$10.50
Purchase #3	$35.72	10.862%	$39.5999	$39.60	$39.60	$39.60
Purchase #4	$130.68	9.336%	$142.8803	$142.88	$142.90	$142.90
Purchase #5	$106.88	4.692%	$111.8948	$111.89	$111.90	$111.90
Purchase #6	$164.99	4.272%	$172.0384	$172.04	$172.05	$172.00
Purchase #7	$45.92	13.213%	$51.9874	$51.99	$52.00	$52.00
7 purchase totals =	$742.82		$801.1763	$801.17	$801.20	$801.20