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	$136.28	6.228%	$144.7675	$144.77	$144.75	$144.80
Purchase #2	$155.96	4.394%	$162.8129	$162.81	$162.80	$162.80
Purchase #3	$204.99	8.502%	$222.4182	$222.42	$222.40	$222.40
Purchase #4	$88.65	13.319%	$100.4573	$100.46	$100.45	$100.50
Purchase #5	$117.93	10.726%	$130.5792	$130.58	$130.60	$130.60
Purchase #6	$81.31	4.781%	$85.1974	$85.20	$85.20	$85.20
Purchase #7	$140.64	9.387%	$153.8419	$153.84	$153.85	$153.80
7 purchase totals =	$925.76		$1,000.0744	$1,000.08	$1,000.05	$1,000.10