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	$18.60	5.867%	$19.6913	$19.69	$19.70	$19.70
Purchase #2	$25.80	5.805%	$27.2977	$27.30	$27.30	$27.30
Purchase #3	$189.52	3.833%	$196.7843	$196.78	$196.80	$196.80
Purchase #4	$97.30	10.432%	$107.4503	$107.45	$107.45	$107.50
Purchase #5	$141.59	9.866%	$155.5593	$155.56	$155.55	$155.60
Purchase #6	$103.44	12.649%	$116.5241	$116.52	$116.50	$116.50
Purchase #7	$140.68	4.148%	$146.5154	$146.52	$146.50	$146.50
7 purchase totals =	$716.93		$769.8224	$769.82	$769.80	$769.90