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	$52.40	6.716%	$55.9192	$55.92	$55.90	$55.90
Purchase #2	$213.41	5.691%	$225.5552	$225.56	$225.55	$225.60
Purchase #3	$196.99	13.340%	$223.2685	$223.27	$223.25	$223.30
Purchase #4	$154.37	8.385%	$167.3139	$167.31	$167.30	$167.30
Purchase #5	$18.95	4.216%	$19.7489	$19.75	$19.75	$19.70
Purchase #6	$87.86	13.112%	$99.3802	$99.38	$99.40	$99.40
Purchase #7	$77.66	6.144%	$82.4314	$82.43	$82.45	$82.40
7 purchase totals =	$801.64		$873.6173	$873.62	$873.60	$873.60