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	$242.41	5.553%	$255.871	$255.87	$255.85	$255.90
Purchase #2	$200.46	5.415%	$211.3149	$211.31	$211.30	$211.30
Purchase #3	$61.29	5.156%	$64.4501	$64.45	$64.45	$64.50
Purchase #4	$134.56	3.302%	$139.0032	$139.00	$139.00	$139.00
Purchase #5	$102.98	9.808%	$113.0803	$113.08	$113.10	$113.10
Purchase #6	$21.30	4.652%	$22.2909	$22.29	$22.30	$22.30
Purchase #7	$19.27	10.628%	$21.318	$21.32	$21.30	$21.30
7 purchase totals =	$782.27		$827.3284	$827.32	$827.30	$827.40