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	$56.42	5.851%	$59.7211	$59.72	$59.70	$59.70
Purchase #2	$9.88	13.772%	$11.2407	$11.24	$11.25	$11.20
Purchase #3	$154.95	7.846%	$167.1074	$167.11	$167.10	$167.10
Purchase #4	$85.96	9.390%	$94.0316	$94.03	$94.05	$94.00
Purchase #5	$12.82	11.380%	$14.2789	$14.28	$14.30	$14.30
Purchase #6	$120.96	6.178%	$128.4329	$128.43	$128.45	$128.40
Purchase #7	$229.51	8.783%	$249.6679	$249.67	$249.65	$249.70
7 purchase totals =	$670.50		$724.4805	$724.48	$724.50	$724.40