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	$247.60	13.139%	$280.1322	$280.13	$280.15	$280.10
Purchase #2	$155.90	11.374%	$173.6321	$173.63	$173.65	$173.60
Purchase #3	$24.31	12.720%	$27.4022	$27.40	$27.40	$27.40
Purchase #4	$19.65	8.798%	$21.3788	$21.38	$21.40	$21.40
Purchase #5	$183.79	6.769%	$196.2307	$196.23	$196.25	$196.20
Purchase #6	$222.69	3.521%	$230.5309	$230.53	$230.55	$230.50
Purchase #7	$61.76	12.582%	$69.5306	$69.53	$69.55	$69.50
7 purchase totals =	$915.70		$998.8375	$998.83	$998.95	$998.70