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	$106.99	12.625%	$120.4975	$120.50	$120.50	$120.50
Purchase #2	$74.71	10.494%	$82.5501	$82.55	$82.55	$82.60
Purchase #3	$122.28	7.555%	$131.5183	$131.52	$131.50	$131.50
Purchase #4	$20.57	9.227%	$22.468	$22.47	$22.45	$22.50
Purchase #5	$207.36	4.665%	$217.0333	$217.03	$217.05	$217.00
Purchase #6	$131.56	8.391%	$142.5992	$142.60	$142.60	$142.60
Purchase #7	$47.41	8.522%	$51.4503	$51.45	$51.45	$51.50
7 purchase totals =	$710.88		$768.1167	$768.12	$768.10	$768.20