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	$46.44	10.644%	$51.3831	$51.38	$51.40	$51.40
Purchase #2	$31.52	8.252%	$34.121	$34.12	$34.10	$34.10
Purchase #3	$129.46	9.303%	$141.5037	$141.50	$141.50	$141.50
Purchase #4	$147.54	7.382%	$158.4314	$158.43	$158.45	$158.40
Purchase #5	$19.97	9.326%	$21.8324	$21.83	$21.85	$21.80
Purchase #6	$213.36	13.402%	$241.9545	$241.95	$241.95	$242.00
Purchase #7	$38.88	8.870%	$42.3287	$42.33	$42.35	$42.30
7 purchase totals =	$627.17		$691.5548	$691.54	$691.60	$691.50