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	$51.97	6.191%	$55.1875	$55.19	$55.20	$55.20
Purchase #2	$100.42	4.615%	$105.0544	$105.05	$105.05	$105.10
Purchase #3	$20.54	6.431%	$21.8609	$21.86	$21.85	$21.90
Purchase #4	$112.99	13.159%	$127.8584	$127.86	$127.85	$127.90
Purchase #5	$123.57	10.303%	$136.3014	$136.30	$136.30	$136.30
Purchase #6	$80.35	7.703%	$86.5394	$86.54	$86.55	$86.50
Purchase #7	$166.64	10.375%	$183.9289	$183.93	$183.95	$183.90
7 purchase totals =	$656.48		$716.7309	$716.73	$716.75	$716.80