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	$138.74	4.773%	$145.3621	$145.36	$145.35	$145.40
Purchase #2	$227.57	10.759%	$252.0543	$252.05	$252.05	$252.10
Purchase #3	$39.50	10.667%	$43.7135	$43.71	$43.70	$43.70
Purchase #4	$239.33	6.549%	$255.0037	$255.00	$255.00	$255.00
Purchase #5	$123.33	9.318%	$134.8219	$134.82	$134.80	$134.80
Purchase #6	$57.36	4.184%	$59.7599	$59.76	$59.75	$59.80
Purchase #7	$219.64	13.420%	$249.1157	$249.12	$249.10	$249.10
7 purchase totals =	$1,045.47		$1,139.8311	$1,139.82	$1,139.75	$1,139.90