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	$34.25	9.759%	$37.5925	$37.59	$37.60	$37.60
Purchase #2	$154.82	8.340%	$167.732	$167.73	$167.75	$167.70
Purchase #3	$117.55	11.435%	$130.9918	$130.99	$131.00	$131.00
Purchase #4	$104.51	12.195%	$117.255	$117.26	$117.25	$117.30
Purchase #5	$11.51	11.304%	$12.8111	$12.81	$12.80	$12.80
Purchase #6	$70.41	11.423%	$78.4529	$78.45	$78.45	$78.50
Purchase #7	$33.61	7.278%	$36.0561	$36.06	$36.05	$36.10
7 purchase totals =	$526.66		$580.8914	$580.89	$580.90	$581.00