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	$80.83	11.656%	$90.2515	$90.25	$90.25	$90.30
Purchase #2	$43.82	6.225%	$46.5478	$46.55	$46.55	$46.50
Purchase #3	$5.75	6.758%	$6.1386	$6.14	$6.15	$6.10
Purchase #4	$103.95	7.253%	$111.4895	$111.49	$111.50	$111.50
Purchase #5	$110.70	10.438%	$122.2549	$122.25	$122.25	$122.30
Purchase #6	$90.98	13.299%	$103.0794	$103.08	$103.10	$103.10
Purchase #7	$14.88	9.196%	$16.2484	$16.25	$16.25	$16.20
7 purchase totals =	$450.91		$496.0101	$496.01	$496.05	$496.00