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	$83.96	9.544%	$91.9731	$91.97	$91.95	$92.00
Purchase #2	$42.69	4.488%	$44.6059	$44.61	$44.60	$44.60
Purchase #3	$115.37	13.738%	$131.2195	$131.22	$131.20	$131.20
Purchase #4	$47.49	8.199%	$51.3837	$51.38	$51.40	$51.40
Purchase #5	$146.65	13.528%	$166.4888	$166.49	$166.50	$166.50
Purchase #6	$50.71	11.139%	$56.3586	$56.36	$56.35	$56.40
Purchase #7	$46.25	7.803%	$49.8589	$49.86	$49.85	$49.90
7 purchase totals =	$533.12		$591.8885	$591.89	$591.85	$592.00