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	$105.91	11.788%	$118.3947	$118.39	$118.40	$118.40
Purchase #2	$128.33	6.226%	$136.3198	$136.32	$136.30	$136.30
Purchase #3	$5.51	13.382%	$6.2473	$6.25	$6.25	$6.20
Purchase #4	$103.74	10.265%	$114.3889	$114.39	$114.40	$114.40
Purchase #5	$29.50	3.333%	$30.4832	$30.48	$30.50	$30.50
Purchase #6	$138.38	6.106%	$146.8295	$146.83	$146.85	$146.80
Purchase #7	$225.45	10.564%	$249.2665	$249.27	$249.25	$249.30
7 purchase totals =	$736.82		$801.9299	$801.93	$801.95	$801.90