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	$48.37	9.352%	$52.8936	$52.89	$52.90	$52.90
Purchase #2	$154.33	7.366%	$165.6979	$165.70	$165.70	$165.70
Purchase #3	$34.34	5.512%	$36.2328	$36.23	$36.25	$36.20
Purchase #4	$60.29	10.323%	$66.5137	$66.51	$66.50	$66.50
Purchase #5	$49.64	13.527%	$56.3548	$56.35	$56.35	$56.40
Purchase #6	$51.38	12.338%	$57.7193	$57.72	$57.70	$57.70
Purchase #7	$98.92	12.224%	$111.012	$111.01	$111.00	$111.00
7 purchase totals =	$497.27		$546.4241	$546.41	$546.40	$546.40