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	$231.71	11.634%	$258.6671	$258.67	$258.65	$258.70
Purchase #2	$178.25	3.436%	$184.3747	$184.37	$184.35	$184.40
Purchase #3	$113.54	8.250%	$122.9071	$122.91	$122.90	$122.90
Purchase #4	$88.51	4.600%	$92.5815	$92.58	$92.60	$92.60
Purchase #5	$143.29	3.225%	$147.9111	$147.91	$147.90	$147.90
Purchase #6	$129.62	12.261%	$145.5127	$145.51	$145.50	$145.50
Purchase #7	$93.61	12.749%	$105.5443	$105.54	$105.55	$105.50
7 purchase totals =	$978.53		$1,057.4985	$1,057.49	$1,057.45	$1,057.50