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	$66.88	6.710%	$71.3676	$71.37	$71.35	$71.40
Purchase #2	$111.28	10.194%	$122.6239	$122.62	$122.60	$122.60
Purchase #3	$243.50	5.399%	$256.6466	$256.65	$256.65	$256.60
Purchase #4	$19.66	7.652%	$21.1644	$21.16	$21.15	$21.20
Purchase #5	$68.71	3.723%	$71.2681	$71.27	$71.25	$71.30
Purchase #6	$179.42	6.760%	$191.5488	$191.55	$191.55	$191.50
Purchase #7	$230.86	6.197%	$245.1664	$245.17	$245.15	$245.20
7 purchase totals =	$920.31		$979.7858	$979.79	$979.70	$979.80