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	$100.88	8.438%	$109.3923	$109.39	$109.40	$109.40
Purchase #2	$105.25	11.662%	$117.5243	$117.52	$117.50	$117.50
Purchase #3	$21.80	7.522%	$23.4398	$23.44	$23.45	$23.40
Purchase #4	$204.51	8.686%	$222.2737	$222.27	$222.25	$222.30
Purchase #5	$100.52	4.291%	$104.8333	$104.83	$104.85	$104.80
Purchase #6	$161.58	9.213%	$176.4664	$176.47	$176.45	$176.50
Purchase #7	$128.92	13.366%	$146.1514	$146.15	$146.15	$146.20
7 purchase totals =	$823.46		$900.0812	$900.07	$900.05	$900.10