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	$12.89	3.729%	$13.3707	$13.37	$13.35	$13.40
Purchase #2	$35.52	10.793%	$39.3537	$39.35	$39.35	$39.40
Purchase #3	$158.40	12.397%	$178.0368	$178.04	$178.05	$178.00
Purchase #4	$31.84	4.193%	$33.1751	$33.18	$33.20	$33.20
Purchase #5	$126.83	3.506%	$131.2767	$131.28	$131.30	$131.30
Purchase #6	$83.64	8.104%	$90.4182	$90.42	$90.40	$90.40
Purchase #7	$178.65	10.474%	$197.3618	$197.36	$197.35	$197.40
7 purchase totals =	$627.77		$682.9930	$683.00	$683.00	$683.10