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	$95.32	4.492%	$99.6018	$99.60	$99.60	$99.60
Purchase #2	$43.61	11.473%	$48.6134	$48.61	$48.60	$48.60
Purchase #3	$46.34	8.253%	$50.1644	$50.16	$50.15	$50.20
Purchase #4	$132.93	4.589%	$139.0302	$139.03	$139.05	$139.00
Purchase #5	$77.74	10.253%	$85.7107	$85.71	$85.70	$85.70
Purchase #6	$82.65	9.541%	$90.5356	$90.54	$90.55	$90.50
Purchase #7	$87.42	13.385%	$99.1212	$99.12	$99.10	$99.10
7 purchase totals =	$566.01		$612.7773	$612.77	$612.75	$612.70