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	$25.71	5.861%	$27.2169	$27.22	$27.20	$27.20
Purchase #2	$178.82	11.117%	$198.6994	$198.70	$198.70	$198.70
Purchase #3	$196.59	9.582%	$215.4273	$215.43	$215.45	$215.40
Purchase #4	$229.91	4.168%	$239.4926	$239.49	$239.50	$239.50
Purchase #5	$45.27	12.322%	$50.8482	$50.85	$50.85	$50.80
Purchase #6	$112.40	13.606%	$127.6931	$127.69	$127.70	$127.70
Purchase #7	$99.75	11.864%	$111.5843	$111.58	$111.60	$111.60
7 purchase totals =	$888.45		$970.9618	$970.96	$971.00	$970.90