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	$12.64	4.129%	$13.1619	$13.16	$13.15	$13.20
Purchase #2	$62.62	7.556%	$67.3516	$67.35	$67.35	$67.40
Purchase #3	$174.68	9.613%	$191.472	$191.47	$191.45	$191.50
Purchase #4	$132.66	6.255%	$140.9579	$140.96	$140.95	$141.00
Purchase #5	$48.73	5.504%	$51.4121	$51.41	$51.40	$51.40
Purchase #6	$15.34	3.413%	$15.8636	$15.86	$15.85	$15.90
Purchase #7	$12.76	4.856%	$13.3796	$13.38	$13.40	$13.40
7 purchase totals =	$459.43		$493.5987	$493.59	$493.55	$493.80