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	$245.97	13.535%	$279.262	$279.26	$279.25	$279.30
Purchase #2	$169.50	6.116%	$179.8666	$179.87	$179.85	$179.90
Purchase #3	$113.35	12.731%	$127.7806	$127.78	$127.80	$127.80
Purchase #4	$134.37	8.288%	$145.5066	$145.51	$145.50	$145.50
Purchase #5	$189.60	9.716%	$208.0215	$208.02	$208.00	$208.00
Purchase #6	$54.33	8.680%	$59.0458	$59.05	$59.05	$59.00
Purchase #7	$224.83	7.874%	$242.5331	$242.53	$242.55	$242.50
7 purchase totals =	$1,131.95		$1,242.0162	$1,242.02	$1,242.00	$1,242.00