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	$103.91	12.200%	$116.587	$116.59	$116.60	$116.60
Purchase #2	$80.62	11.689%	$90.0437	$90.04	$90.05	$90.00
Purchase #3	$239.30	10.542%	$264.527	$264.53	$264.55	$264.50
Purchase #4	$126.41	13.238%	$143.1442	$143.14	$143.15	$143.10
Purchase #5	$39.25	9.476%	$42.9693	$42.97	$42.95	$43.00
Purchase #6	$171.95	6.238%	$182.6762	$182.68	$182.70	$182.70
Purchase #7	$228.97	12.643%	$257.9187	$257.92	$257.90	$257.90
7 purchase totals =	$990.41		$1,097.8661	$1,097.87	$1,097.90	$1,097.80