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	$79.32	12.714%	$89.4047	$89.40	$89.40	$89.40
Purchase #2	$94.69	7.813%	$102.0881	$102.09	$102.10	$102.10
Purchase #3	$250.32	11.824%	$279.9178	$279.92	$279.90	$279.90
Purchase #4	$107.90	12.581%	$121.4749	$121.47	$121.45	$121.50
Purchase #5	$117.44	11.672%	$131.1476	$131.15	$131.15	$131.10
Purchase #6	$174.66	7.344%	$187.487	$187.49	$187.50	$187.50
Purchase #7	$183.60	13.646%	$208.6541	$208.65	$208.65	$208.70
7 purchase totals =	$1,007.93		$1,120.1742	$1,120.17	$1,120.15	$1,120.20