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	$37.72	13.254%	$42.7194	$42.72	$42.70	$42.70
Purchase #2	$110.68	12.278%	$124.2693	$124.27	$124.25	$124.30
Purchase #3	$116.72	13.387%	$132.3453	$132.35	$132.35	$132.30
Purchase #4	$19.82	11.664%	$22.1318	$22.13	$22.15	$22.10
Purchase #5	$16.38	6.256%	$17.4047	$17.40	$17.40	$17.40
Purchase #6	$117.44	9.334%	$128.4018	$128.40	$128.40	$128.40
Purchase #7	$40.36	7.435%	$43.3608	$43.36	$43.35	$43.40
7 purchase totals =	$459.12		$510.6331	$510.63	$510.60	$510.60