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	$97.43	12.275%	$109.3895	$109.39	$109.40	$109.40
Purchase #2	$129.47	6.709%	$138.1561	$138.16	$138.15	$138.20
Purchase #3	$87.56	3.219%	$90.3786	$90.38	$90.40	$90.40
Purchase #4	$216.66	11.264%	$241.0646	$241.06	$241.05	$241.10
Purchase #5	$78.36	4.865%	$82.1722	$82.17	$82.15	$82.20
Purchase #6	$130.38	13.551%	$148.0478	$148.05	$148.05	$148.00
Purchase #7	$73.82	12.543%	$83.0792	$83.08	$83.10	$83.10
7 purchase totals =	$813.68		$892.2880	$892.29	$892.30	$892.40