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	$113.32	12.301%	$127.2595	$127.26	$127.25	$127.30
Purchase #2	$94.93	6.224%	$100.8384	$100.84	$100.85	$100.80
Purchase #3	$95.42	7.728%	$102.7941	$102.79	$102.80	$102.80
Purchase #4	$246.37	10.612%	$272.5148	$272.51	$272.50	$272.50
Purchase #5	$98.69	12.513%	$111.0391	$111.04	$111.05	$111.00
Purchase #6	$16.90	3.289%	$17.4558	$17.46	$17.45	$17.50
Purchase #7	$122.80	11.213%	$136.5696	$136.57	$136.55	$136.60
7 purchase totals =	$788.43		$868.4713	$868.47	$868.45	$868.50