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	$78.87	13.819%	$89.769	$89.77	$89.75	$89.80
Purchase #2	$157.95	7.316%	$169.5056	$169.51	$169.50	$169.50
Purchase #3	$14.45	8.262%	$15.6439	$15.64	$15.65	$15.60
Purchase #4	$188.43	9.117%	$205.6092	$205.61	$205.60	$205.60
Purchase #5	$82.37	12.261%	$92.4694	$92.47	$92.45	$92.50
Purchase #6	$155.26	13.218%	$175.7823	$175.78	$175.80	$175.80
Purchase #7	$108.50	3.398%	$112.1868	$112.19	$112.20	$112.20
7 purchase totals =	$785.83		$860.9662	$860.97	$860.95	$861.00