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	$19.71	9.512%	$21.5848	$21.58	$21.60	$21.60
Purchase #2	$163.43	9.504%	$178.9624	$178.96	$178.95	$179.00
Purchase #3	$220.69	11.750%	$246.6211	$246.62	$246.60	$246.60
Purchase #4	$58.94	4.759%	$61.745	$61.75	$61.75	$61.70
Purchase #5	$179.94	4.730%	$188.4512	$188.45	$188.45	$188.50
Purchase #6	$99.80	11.833%	$111.6093	$111.61	$111.60	$111.60
Purchase #7	$236.48	8.212%	$255.8997	$255.90	$255.90	$255.90
7 purchase totals =	$978.99		$1,064.8735	$1,064.87	$1,064.85	$1,064.90