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	$55.77	12.358%	$62.6621	$62.66	$62.65	$62.70
Purchase #2	$173.66	11.760%	$194.0824	$194.08	$194.10	$194.10
Purchase #3	$45.72	5.266%	$48.1276	$48.13	$48.15	$48.10
Purchase #4	$118.90	7.754%	$128.1195	$128.12	$128.10	$128.10
Purchase #5	$39.95	13.261%	$45.2478	$45.25	$45.25	$45.20
Purchase #6	$45.54	13.253%	$51.5754	$51.58	$51.60	$51.60
Purchase #7	$72.29	11.302%	$80.4602	$80.46	$80.45	$80.50
7 purchase totals =	$551.83		$610.2750	$610.28	$610.30	$610.30