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	$139.63	3.321%	$144.2671	$144.27	$144.25	$144.30
Purchase #2	$66.77	7.849%	$72.0108	$72.01	$72.00	$72.00
Purchase #3	$46.98	4.572%	$49.1279	$49.13	$49.15	$49.10
Purchase #4	$97.98	4.561%	$102.4489	$102.45	$102.45	$102.40
Purchase #5	$221.32	7.298%	$237.4719	$237.47	$237.45	$237.50
Purchase #6	$90.81	7.866%	$97.9531	$97.95	$97.95	$98.00
Purchase #7	$131.98	7.154%	$141.4218	$141.42	$141.40	$141.40
7 purchase totals =	$795.47		$844.7015	$844.70	$844.65	$844.70