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	$128.85	13.204%	$145.8634	$145.86	$145.85	$145.90
Purchase #2	$138.79	8.168%	$150.1264	$150.13	$150.15	$150.10
Purchase #3	$117.70	9.280%	$128.6226	$128.62	$128.60	$128.60
Purchase #4	$239.58	11.387%	$266.861	$266.86	$266.85	$266.90
Purchase #5	$39.65	11.168%	$44.0781	$44.08	$44.10	$44.10
Purchase #6	$38.42	10.710%	$42.5348	$42.53	$42.55	$42.50
Purchase #7	$85.32	10.596%	$94.3605	$94.36	$94.35	$94.40
7 purchase totals =	$788.31		$872.4468	$872.44	$872.45	$872.50