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	$16.97	5.809%	$17.9558	$17.96	$17.95	$18.00
Purchase #2	$248.68	11.579%	$277.4747	$277.47	$277.45	$277.50
Purchase #3	$104.80	11.341%	$116.6854	$116.69	$116.70	$116.70
Purchase #4	$55.61	12.677%	$62.6597	$62.66	$62.65	$62.70
Purchase #5	$196.28	13.572%	$222.9191	$222.92	$222.90	$222.90
Purchase #6	$131.50	10.316%	$145.0655	$145.07	$145.05	$145.10
Purchase #7	$235.74	8.407%	$255.5587	$255.56	$255.55	$255.60
7 purchase totals =	$989.58		$1,098.3189	$1,098.33	$1,098.25	$1,098.50