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	$213.55	6.829%	$228.1333	$228.13	$228.15	$228.10
Purchase #2	$222.55	7.328%	$238.8585	$238.86	$238.85	$238.90
Purchase #3	$9.31	10.469%	$10.2847	$10.28	$10.30	$10.30
Purchase #4	$54.82	8.525%	$59.4934	$59.49	$59.50	$59.50
Purchase #5	$12.26	11.433%	$13.6617	$13.66	$13.65	$13.70
Purchase #6	$29.65	10.405%	$32.7351	$32.74	$32.75	$32.70
Purchase #7	$17.89	11.843%	$20.0087	$20.01	$20.00	$20.00
7 purchase totals =	$560.03		$603.1754	$603.17	$603.20	$603.20