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	$172.79	9.139%	$188.5813	$188.58	$188.60	$188.60
Purchase #2	$80.58	5.522%	$85.0296	$85.03	$85.05	$85.00
Purchase #3	$112.42	9.577%	$123.1865	$123.19	$123.20	$123.20
Purchase #4	$133.75	13.848%	$152.2717	$152.27	$152.25	$152.30
Purchase #5	$236.82	9.791%	$260.007	$260.01	$260.00	$260.00
Purchase #6	$27.59	8.323%	$29.8863	$29.89	$29.90	$29.90
Purchase #7	$127.98	13.272%	$144.9655	$144.97	$144.95	$145.00
7 purchase totals =	$891.93		$983.9279	$983.94	$983.95	$984.00