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	$35.25	11.695%	$39.3725	$39.37	$39.35	$39.40
Purchase #2	$78.53	10.189%	$86.5314	$86.53	$86.55	$86.50
Purchase #3	$45.61	12.449%	$51.288	$51.29	$51.30	$51.30
Purchase #4	$143.97	7.816%	$155.2227	$155.22	$155.20	$155.20
Purchase #5	$94.43	6.208%	$100.2922	$100.29	$100.30	$100.30
Purchase #6	$142.52	5.373%	$150.1776	$150.18	$150.20	$150.20
Purchase #7	$96.53	8.639%	$104.8692	$104.87	$104.85	$104.90
7 purchase totals =	$636.84		$687.7536	$687.75	$687.75	$687.80