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	$9.79	10.621%	$10.8298	$10.83	$10.85	$10.80
Purchase #2	$184.35	7.540%	$198.25	$198.25	$198.25	$198.30
Purchase #3	$55.67	10.870%	$61.7213	$61.72	$61.70	$61.70
Purchase #4	$249.59	3.231%	$257.6543	$257.65	$257.65	$257.70
Purchase #5	$31.66	5.665%	$33.4535	$33.45	$33.45	$33.50
Purchase #6	$11.91	10.166%	$13.1208	$13.12	$13.10	$13.10
Purchase #7	$46.40	4.373%	$48.4291	$48.43	$48.45	$48.40
7 purchase totals =	$589.37		$623.4588	$623.45	$623.45	$623.50