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	$55.53	8.597%	$60.3039	$60.30	$60.30	$60.30
Purchase #2	$132.53	10.659%	$146.6564	$146.66	$146.65	$146.70
Purchase #3	$232.64	7.245%	$249.4948	$249.49	$249.50	$249.50
Purchase #4	$89.94	10.347%	$99.2461	$99.25	$99.25	$99.20
Purchase #5	$21.72	12.354%	$24.4033	$24.40	$24.40	$24.40
Purchase #6	$250.42	9.358%	$273.8543	$273.85	$273.85	$273.90
Purchase #7	$41.45	8.747%	$45.0756	$45.08	$45.10	$45.10
7 purchase totals =	$824.23		$899.0344	$899.03	$899.05	$899.10