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	$247.67	3.245%	$255.7069	$255.71	$255.70	$255.70
Purchase #2	$118.72	10.841%	$131.5904	$131.59	$131.60	$131.60
Purchase #3	$72.86	10.826%	$80.7478	$80.75	$80.75	$80.70
Purchase #4	$112.67	6.421%	$119.9045	$119.90	$119.90	$119.90
Purchase #5	$42.61	11.769%	$47.6248	$47.62	$47.60	$47.60
Purchase #6	$201.35	7.610%	$216.6727	$216.67	$216.65	$216.70
Purchase #7	$59.86	13.566%	$67.9806	$67.98	$68.00	$68.00
7 purchase totals =	$855.74		$920.2277	$920.22	$920.20	$920.20