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	$37.88	13.768%	$43.0953	$43.10	$43.10	$43.10
Purchase #2	$37.36	6.529%	$39.7992	$39.80	$39.80	$39.80
Purchase #3	$181.85	13.406%	$206.2288	$206.23	$206.25	$206.20
Purchase #4	$231.94	10.742%	$256.855	$256.86	$256.85	$256.90
Purchase #5	$226.94	9.721%	$249.0008	$249.00	$249.00	$249.00
Purchase #6	$207.98	13.536%	$236.1322	$236.13	$236.15	$236.10
Purchase #7	$49.43	10.192%	$54.4679	$54.47	$54.45	$54.50
7 purchase totals =	$973.38		$1,085.5792	$1,085.59	$1,085.60	$1,085.60