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	$17.91	9.376%	$19.5892	$19.59	$19.60	$19.60
Purchase #2	$76.95	9.566%	$84.311	$84.31	$84.30	$84.30
Purchase #3	$100.52	4.709%	$105.2535	$105.25	$105.25	$105.30
Purchase #4	$78.70	5.264%	$82.8428	$82.84	$82.85	$82.80
Purchase #5	$36.39	8.302%	$39.4111	$39.41	$39.40	$39.40
Purchase #6	$43.40	10.777%	$48.0772	$48.08	$48.10	$48.10
Purchase #7	$124.38	3.547%	$128.7918	$128.79	$128.80	$128.80
7 purchase totals =	$478.25		$508.2766	$508.27	$508.30	$508.30