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	$230.80	12.469%	$259.5785	$259.58	$259.60	$259.60
Purchase #2	$241.45	12.604%	$271.8824	$271.88	$271.90	$271.90
Purchase #3	$187.53	3.184%	$193.501	$193.50	$193.50	$193.50
Purchase #4	$64.92	12.290%	$72.8987	$72.90	$72.90	$72.90
Purchase #5	$193.63	9.213%	$211.4691	$211.47	$211.45	$211.50
Purchase #6	$228.87	11.773%	$255.8149	$255.81	$255.80	$255.80
Purchase #7	$135.50	12.416%	$152.3237	$152.32	$152.30	$152.30
7 purchase totals =	$1,282.70		$1,417.4683	$1,417.46	$1,417.45	$1,417.50