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	$20.29	3.104%	$20.9198	$20.92	$20.90	$20.90
Purchase #2	$112.63	4.185%	$117.3436	$117.34	$117.35	$117.30
Purchase #3	$51.67	5.763%	$54.6477	$54.65	$54.65	$54.60
Purchase #4	$75.71	13.443%	$85.8877	$85.89	$85.90	$85.90
Purchase #5	$49.40	8.166%	$53.434	$53.43	$53.45	$53.40
Purchase #6	$100.51	9.379%	$109.9368	$109.94	$109.95	$109.90
Purchase #7	$119.81	4.142%	$124.7725	$124.77	$124.75	$124.80
7 purchase totals =	$530.02		$566.9421	$566.94	$566.95	$566.80