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	$127.27	8.151%	$137.6438	$137.64	$137.65	$137.60
Purchase #2	$25.88	10.490%	$28.5948	$28.59	$28.60	$28.60
Purchase #3	$44.81	13.333%	$50.7845	$50.78	$50.80	$50.80
Purchase #4	$166.42	11.830%	$186.1075	$186.11	$186.10	$186.10
Purchase #5	$105.70	12.127%	$118.5182	$118.52	$118.50	$118.50
Purchase #6	$80.73	5.687%	$85.3211	$85.32	$85.30	$85.30
Purchase #7	$172.60	5.113%	$181.425	$181.43	$181.45	$181.40
7 purchase totals =	$723.41		$788.3949	$788.39	$788.40	$788.30