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	$132.64	5.307%	$139.6792	$139.68	$139.70	$139.70
Purchase #2	$245.27	12.847%	$276.7798	$276.78	$276.80	$276.80
Purchase #3	$55.41	11.618%	$61.8475	$61.85	$61.85	$61.80
Purchase #4	$46.88	4.829%	$49.1438	$49.14	$49.15	$49.10
Purchase #5	$139.98	4.323%	$146.0313	$146.03	$146.05	$146.00
Purchase #6	$63.94	13.397%	$72.506	$72.51	$72.50	$72.50
Purchase #7	$139.88	5.386%	$147.4139	$147.41	$147.40	$147.40
7 purchase totals =	$824.00		$893.4015	$893.40	$893.45	$893.30