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	$45.37	8.819%	$49.3712	$49.37	$49.35	$49.40
Purchase #2	$104.69	3.533%	$108.3887	$108.39	$108.40	$108.40
Purchase #3	$79.73	12.356%	$89.5814	$89.58	$89.60	$89.60
Purchase #4	$178.74	9.843%	$196.3334	$196.33	$196.35	$196.30
Purchase #5	$187.81	3.602%	$194.5749	$194.57	$194.55	$194.60
Purchase #6	$148.85	3.488%	$154.0419	$154.04	$154.05	$154.00
Purchase #7	$175.28	13.846%	$199.5493	$199.55	$199.55	$199.50
7 purchase totals =	$920.47		$991.8408	$991.83	$991.85	$991.80