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	$17.65	7.181%	$18.9174	$18.92	$18.90	$18.90
Purchase #2	$200.43	7.573%	$215.6086	$215.61	$215.60	$215.60
Purchase #3	$96.47	7.388%	$103.5972	$103.60	$103.60	$103.60
Purchase #4	$179.45	6.258%	$190.68	$190.68	$190.70	$190.70
Purchase #5	$47.78	7.867%	$51.5389	$51.54	$51.55	$51.50
Purchase #6	$129.58	11.874%	$144.9663	$144.97	$144.95	$145.00
Purchase #7	$97.30	5.460%	$102.6126	$102.61	$102.60	$102.60
7 purchase totals =	$768.66		$827.9210	$827.93	$827.90	$827.90