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	$199.91	9.620%	$219.1413	$219.14	$219.15	$219.10
Purchase #2	$82.59	4.235%	$86.0877	$86.09	$86.10	$86.10
Purchase #3	$224.96	8.624%	$244.3606	$244.36	$244.35	$244.40
Purchase #4	$100.29	11.159%	$111.4814	$111.48	$111.50	$111.50
Purchase #5	$26.90	9.388%	$29.4254	$29.43	$29.45	$29.40
Purchase #6	$66.77	4.326%	$69.6585	$69.66	$69.65	$69.70
Purchase #7	$134.38	13.689%	$152.7753	$152.78	$152.80	$152.80
7 purchase totals =	$835.80		$912.9302	$912.94	$913.00	$913.00