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	$136.85	12.230%	$153.5868	$153.59	$153.60	$153.60
Purchase #2	$237.93	7.397%	$255.5297	$255.53	$255.55	$255.50
Purchase #3	$81.72	4.693%	$85.5551	$85.56	$85.55	$85.60
Purchase #4	$17.33	6.389%	$18.4372	$18.44	$18.45	$18.40
Purchase #5	$85.70	7.675%	$92.2775	$92.28	$92.30	$92.30
Purchase #6	$196.95	3.749%	$204.3337	$204.33	$204.35	$204.30
Purchase #7	$95.82	4.376%	$100.0131	$100.01	$100.00	$100.00
7 purchase totals =	$852.30		$909.7331	$909.74	$909.80	$909.70