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	$29.70	8.710%	$32.2869	$32.29	$32.30	$32.30
Purchase #2	$140.53	5.689%	$148.5248	$148.52	$148.50	$148.50
Purchase #3	$248.59	3.368%	$256.9625	$256.96	$256.95	$257.00
Purchase #4	$164.77	4.713%	$172.5356	$172.54	$172.55	$172.50
Purchase #5	$111.69	3.469%	$115.5645	$115.56	$115.55	$115.60
Purchase #6	$139.79	12.260%	$156.9283	$156.93	$156.95	$156.90
Purchase #7	$140.92	12.425%	$158.4293	$158.43	$158.45	$158.40
7 purchase totals =	$975.99		$1,041.2319	$1,041.23	$1,041.25	$1,041.20