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	$49.75	11.755%	$55.5981	$55.60	$55.60	$55.60
Purchase #2	$240.90	7.261%	$258.3917	$258.39	$258.40	$258.40
Purchase #3	$87.46	4.725%	$91.5925	$91.59	$91.60	$91.60
Purchase #4	$230.66	3.112%	$237.8381	$237.84	$237.85	$237.80
Purchase #5	$29.69	9.681%	$32.5643	$32.56	$32.55	$32.60
Purchase #6	$194.90	10.789%	$215.9278	$215.93	$215.95	$215.90
Purchase #7	$57.89	13.346%	$65.616	$65.62	$65.60	$65.60
7 purchase totals =	$891.25		$957.5285	$957.53	$957.55	$957.50