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	$18.95	12.606%	$21.3388	$21.34	$21.35	$21.30
Purchase #2	$134.32	6.526%	$143.0857	$143.09	$143.10	$143.10
Purchase #3	$86.63	3.694%	$89.8301	$89.83	$89.85	$89.80
Purchase #4	$203.37	11.809%	$227.386	$227.39	$227.40	$227.40
Purchase #5	$222.50	12.481%	$250.2702	$250.27	$250.25	$250.30
Purchase #6	$58.56	13.296%	$66.3461	$66.35	$66.35	$66.30
Purchase #7	$106.60	10.569%	$117.8666	$117.87	$117.85	$117.90
7 purchase totals =	$830.93		$916.1235	$916.14	$916.15	$916.10