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	$112.74	3.377%	$116.5472	$116.55	$116.55	$116.50
Purchase #2	$152.38	8.593%	$165.474	$165.47	$165.45	$165.50
Purchase #3	$177.99	10.170%	$196.0916	$196.09	$196.10	$196.10
Purchase #4	$55.46	9.389%	$60.6671	$60.67	$60.65	$60.70
Purchase #5	$107.77	10.624%	$119.2195	$119.22	$119.20	$119.20
Purchase #6	$40.90	12.269%	$45.918	$45.92	$45.90	$45.90
Purchase #7	$173.51	3.548%	$179.6661	$179.67	$179.65	$179.70
7 purchase totals =	$820.75		$883.5835	$883.59	$883.50	$883.60