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	$25.78	10.170%	$28.4018	$28.40	$28.40	$28.40
Purchase #2	$69.95	3.838%	$72.6347	$72.63	$72.65	$72.60
Purchase #3	$31.32	10.800%	$34.7026	$34.70	$34.70	$34.70
Purchase #4	$172.93	9.578%	$189.4932	$189.49	$189.50	$189.50
Purchase #5	$78.79	13.581%	$89.4905	$89.49	$89.50	$89.50
Purchase #6	$104.31	10.521%	$115.2845	$115.28	$115.30	$115.30
Purchase #7	$175.40	3.849%	$182.1511	$182.15	$182.15	$182.20
7 purchase totals =	$658.48		$712.1584	$712.14	$712.20	$712.20