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	$249.76	3.466%	$258.4167	$258.42	$258.40	$258.40
Purchase #2	$76.63	10.616%	$84.765	$84.77	$84.75	$84.80
Purchase #3	$34.45	7.118%	$36.9022	$36.90	$36.90	$36.90
Purchase #4	$240.54	6.218%	$255.4968	$255.50	$255.50	$255.50
Purchase #5	$38.92	12.700%	$43.8628	$43.86	$43.85	$43.90
Purchase #6	$97.25	6.859%	$103.9204	$103.92	$103.90	$103.90
Purchase #7	$40.41	9.284%	$44.1617	$44.16	$44.15	$44.20
7 purchase totals =	$777.96		$827.5256	$827.53	$827.45	$827.60