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	$38.95	6.544%	$41.4989	$41.50	$41.50	$41.50
Purchase #2	$159.33	10.870%	$176.6492	$176.65	$176.65	$176.60
Purchase #3	$137.49	8.462%	$149.1244	$149.12	$149.10	$149.10
Purchase #4	$16.35	10.325%	$18.0381	$18.04	$18.05	$18.00
Purchase #5	$146.46	12.693%	$165.0502	$165.05	$165.05	$165.10
Purchase #6	$82.35	10.228%	$90.7728	$90.77	$90.75	$90.80
Purchase #7	$18.38	5.778%	$19.442	$19.44	$19.45	$19.40
7 purchase totals =	$599.31		$660.5756	$660.57	$660.55	$660.50