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	$242.96	8.515%	$263.648	$263.65	$263.65	$263.60
Purchase #2	$42.70	12.863%	$48.1925	$48.19	$48.20	$48.20
Purchase #3	$70.28	12.215%	$78.8647	$78.86	$78.85	$78.90
Purchase #4	$121.52	7.711%	$130.8904	$130.89	$130.90	$130.90
Purchase #5	$86.42	10.523%	$95.514	$95.51	$95.50	$95.50
Purchase #6	$43.75	5.468%	$46.1423	$46.14	$46.15	$46.10
Purchase #7	$39.87	13.737%	$45.3469	$45.35	$45.35	$45.30
7 purchase totals =	$647.50		$708.5988	$708.59	$708.60	$708.50