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	$51.66	7.465%	$55.5164	$55.52	$55.50	$55.50
Purchase #2	$15.30	8.443%	$16.5918	$16.59	$16.60	$16.60
Purchase #3	$69.32	13.725%	$78.8342	$78.83	$78.85	$78.80
Purchase #4	$89.59	4.666%	$93.7703	$93.77	$93.75	$93.80
Purchase #5	$75.91	5.539%	$80.1147	$80.11	$80.10	$80.10
Purchase #6	$53.62	6.861%	$57.2989	$57.30	$57.30	$57.30
Purchase #7	$171.91	7.364%	$184.5695	$184.57	$184.55	$184.60
7 purchase totals =	$527.31		$566.6958	$566.69	$566.65	$566.70