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	$76.60	8.703%	$83.2665	$83.27	$83.25	$83.30
Purchase #2	$90.69	10.440%	$100.158	$100.16	$100.15	$100.20
Purchase #3	$81.83	5.655%	$86.4575	$86.46	$86.45	$86.50
Purchase #4	$101.32	11.761%	$113.2362	$113.24	$113.25	$113.20
Purchase #5	$100.86	11.395%	$112.353	$112.35	$112.35	$112.40
Purchase #6	$117.32	5.816%	$124.1433	$124.14	$124.15	$124.10
Purchase #7	$146.57	8.667%	$159.2732	$159.27	$159.25	$159.30
7 purchase totals =	$715.19		$778.8877	$778.89	$778.85	$779.00