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	$239.41	11.729%	$267.4904	$267.49	$267.50	$267.50
Purchase #2	$213.62	4.512%	$223.2585	$223.26	$223.25	$223.30
Purchase #3	$213.48	11.665%	$238.3824	$238.38	$238.40	$238.40
Purchase #4	$131.41	6.227%	$139.5929	$139.59	$139.60	$139.60
Purchase #5	$173.92	11.761%	$194.3747	$194.37	$194.35	$194.40
Purchase #6	$70.82	13.433%	$80.3333	$80.33	$80.35	$80.30
Purchase #7	$26.30	10.746%	$29.1262	$29.13	$29.15	$29.10
7 purchase totals =	$1,068.96		$1,172.5584	$1,172.55	$1,172.60	$1,172.60