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	$216.91	3.121%	$223.6798	$223.68	$223.70	$223.70
Purchase #2	$70.93	10.577%	$78.4323	$78.43	$78.45	$78.40
Purchase #3	$120.64	6.692%	$128.7132	$128.71	$128.70	$128.70
Purchase #4	$154.34	7.675%	$166.1856	$166.19	$166.20	$166.20
Purchase #5	$32.46	10.294%	$35.8014	$35.80	$35.80	$35.80
Purchase #6	$38.38	5.534%	$40.5039	$40.50	$40.50	$40.50
Purchase #7	$120.72	9.542%	$132.2391	$132.24	$132.25	$132.20
7 purchase totals =	$754.38		$805.5553	$805.55	$805.60	$805.50