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	$59.78	12.497%	$67.2507	$67.25	$67.25	$67.30
Purchase #2	$116.37	12.531%	$130.9523	$130.95	$130.95	$131.00
Purchase #3	$132.41	7.854%	$142.8095	$142.81	$142.80	$142.80
Purchase #4	$38.40	3.701%	$39.8212	$39.82	$39.80	$39.80
Purchase #5	$90.83	4.470%	$94.8901	$94.89	$94.90	$94.90
Purchase #6	$82.69	9.151%	$90.257	$90.26	$90.25	$90.30
Purchase #7	$81.85	5.171%	$86.0825	$86.08	$86.10	$86.10
7 purchase totals =	$602.33		$652.0633	$652.06	$652.05	$652.20