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	$234.32	12.473%	$263.5467	$263.55	$263.55	$263.50
Purchase #2	$140.68	9.508%	$154.0559	$154.06	$154.05	$154.10
Purchase #3	$34.36	10.452%	$37.9513	$37.95	$37.95	$38.00
Purchase #4	$17.39	3.833%	$18.0566	$18.06	$18.05	$18.10
Purchase #5	$30.95	12.680%	$34.8745	$34.87	$34.85	$34.90
Purchase #6	$120.32	5.235%	$126.6188	$126.62	$126.60	$126.60
Purchase #7	$127.58	3.289%	$131.7761	$131.78	$131.80	$131.80
7 purchase totals =	$705.60		$766.8799	$766.89	$766.85	$767.00