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	$105.71	5.866%	$111.9109	$111.91	$111.90	$111.90
Purchase #2	$12.58	4.479%	$13.1435	$13.14	$13.15	$13.10
Purchase #3	$229.85	4.174%	$239.4439	$239.44	$239.45	$239.40
Purchase #4	$156.71	6.288%	$166.5639	$166.56	$166.55	$166.60
Purchase #5	$220.45	12.822%	$248.7161	$248.72	$248.70	$248.70
Purchase #6	$158.91	3.516%	$164.4973	$164.50	$164.50	$164.50
Purchase #7	$22.60	10.404%	$24.9513	$24.95	$24.95	$25.00
7 purchase totals =	$906.81		$969.2269	$969.22	$969.20	$969.20