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	$7.50	5.608%	$7.9206	$7.92	$7.90	$7.90
Purchase #2	$48.38	12.725%	$54.5364	$54.54	$54.55	$54.50
Purchase #3	$250.42	8.103%	$270.7115	$270.71	$270.70	$270.70
Purchase #4	$48.83	9.750%	$53.5909	$53.59	$53.60	$53.60
Purchase #5	$104.83	4.357%	$109.3974	$109.40	$109.40	$109.40
Purchase #6	$193.70	11.474%	$215.9251	$215.93	$215.95	$215.90
Purchase #7	$230.79	12.568%	$259.7957	$259.80	$259.80	$259.80
7 purchase totals =	$884.45		$971.8776	$971.89	$971.90	$971.80