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	$68.96	3.610%	$71.4495	$71.45	$71.45	$71.40
Purchase #2	$113.86	13.450%	$129.1742	$129.17	$129.15	$129.20
Purchase #3	$92.58	7.404%	$99.4346	$99.43	$99.45	$99.40
Purchase #4	$111.35	3.724%	$115.4967	$115.50	$115.50	$115.50
Purchase #5	$194.45	3.291%	$200.8493	$200.85	$200.85	$200.80
Purchase #6	$215.65	9.574%	$236.2963	$236.30	$236.30	$236.30
Purchase #7	$128.65	7.218%	$137.936	$137.94	$137.95	$137.90
7 purchase totals =	$925.50		$990.6366	$990.64	$990.65	$990.50