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	$64.34	12.669%	$72.4912	$72.49	$72.50	$72.50
Purchase #2	$92.96	9.491%	$101.7828	$101.78	$101.80	$101.80
Purchase #3	$201.75	10.853%	$223.6459	$223.65	$223.65	$223.60
Purchase #4	$83.47	8.510%	$90.5733	$90.57	$90.55	$90.60
Purchase #5	$244.51	13.427%	$277.3404	$277.34	$277.35	$277.30
Purchase #6	$145.59	8.395%	$157.8123	$157.81	$157.80	$157.80
Purchase #7	$160.53	10.198%	$176.9008	$176.90	$176.90	$176.90
7 purchase totals =	$993.15		$1,100.5467	$1,100.54	$1,100.55	$1,100.50