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	$13.77	10.492%	$15.2147	$15.21	$15.20	$15.20
Purchase #2	$150.25	13.392%	$170.3715	$170.37	$170.35	$170.40
Purchase #3	$14.69	8.202%	$15.8949	$15.89	$15.90	$15.90
Purchase #4	$80.59	11.869%	$90.1552	$90.16	$90.15	$90.20
Purchase #5	$35.75	12.667%	$40.2785	$40.28	$40.30	$40.30
Purchase #6	$69.25	8.135%	$74.8835	$74.88	$74.90	$74.90
Purchase #7	$250.62	9.142%	$273.5317	$273.53	$273.55	$273.50
7 purchase totals =	$614.92		$680.3300	$680.32	$680.35	$680.40