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	$99.66	11.682%	$111.3023	$111.30	$111.30	$111.30
Purchase #2	$128.39	8.691%	$139.5484	$139.55	$139.55	$139.50
Purchase #3	$213.53	7.787%	$230.1576	$230.16	$230.15	$230.20
Purchase #4	$30.68	5.735%	$32.4395	$32.44	$32.45	$32.40
Purchase #5	$29.47	10.581%	$32.5882	$32.59	$32.60	$32.60
Purchase #6	$170.69	9.726%	$187.2913	$187.29	$187.30	$187.30
Purchase #7	$69.88	9.761%	$76.701	$76.70	$76.70	$76.70
7 purchase totals =	$742.30		$810.0283	$810.03	$810.05	$810.00