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	$79.89	3.193%	$82.4409	$82.44	$82.45	$82.40
Purchase #2	$103.47	3.714%	$107.3129	$107.31	$107.30	$107.30
Purchase #3	$91.58	9.711%	$100.4733	$100.47	$100.45	$100.50
Purchase #4	$217.95	12.282%	$244.7186	$244.72	$244.70	$244.70
Purchase #5	$12.66	3.299%	$13.0777	$13.08	$13.10	$13.10
Purchase #6	$76.42	7.789%	$82.3724	$82.37	$82.35	$82.40
Purchase #7	$16.67	8.443%	$18.0774	$18.08	$18.10	$18.10
7 purchase totals =	$598.64		$648.4732	$648.47	$648.45	$648.50