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	$14.67	7.851%	$15.8217	$15.82	$15.80	$15.80
Purchase #2	$43.81	6.645%	$46.7212	$46.72	$46.70	$46.70
Purchase #3	$176.42	5.329%	$185.8214	$185.82	$185.80	$185.80
Purchase #4	$39.27	11.834%	$43.9172	$43.92	$43.90	$43.90
Purchase #5	$90.35	13.839%	$102.8535	$102.85	$102.85	$102.90
Purchase #6	$122.78	9.492%	$134.4343	$134.43	$134.45	$134.40
Purchase #7	$23.31	9.204%	$25.4555	$25.46	$25.45	$25.50
7 purchase totals =	$510.61		$555.0248	$555.02	$554.95	$555.00