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	$234.54	7.201%	$251.4292	$251.43	$251.45	$251.40
Purchase #2	$127.65	10.378%	$140.8975	$140.90	$140.90	$140.90
Purchase #3	$54.54	8.491%	$59.171	$59.17	$59.15	$59.20
Purchase #4	$153.62	10.139%	$169.1955	$169.20	$169.20	$169.20
Purchase #5	$174.26	9.282%	$190.4348	$190.43	$190.45	$190.40
Purchase #6	$70.54	8.379%	$76.4505	$76.45	$76.45	$76.50
Purchase #7	$25.32	9.792%	$27.7993	$27.80	$27.80	$27.80
7 purchase totals =	$840.47		$915.3778	$915.38	$915.40	$915.40