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	$7.50	4.759%	$7.8569	$7.86	$7.85	$7.90
Purchase #2	$50.32	13.483%	$57.1046	$57.10	$57.10	$57.10
Purchase #3	$110.57	10.777%	$122.4861	$122.49	$122.50	$122.50
Purchase #4	$72.78	8.244%	$78.78	$78.78	$78.80	$78.80
Purchase #5	$50.50	11.189%	$56.1504	$56.15	$56.15	$56.20
Purchase #6	$210.77	8.812%	$229.3431	$229.34	$229.35	$229.30
Purchase #7	$29.29	10.852%	$32.4686	$32.47	$32.45	$32.50
7 purchase totals =	$531.73		$584.1897	$584.19	$584.20	$584.30