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	$107.47	7.291%	$115.3056	$115.31	$115.30	$115.30
Purchase #2	$202.40	9.807%	$222.2494	$222.25	$222.25	$222.20
Purchase #3	$48.40	12.393%	$54.3982	$54.40	$54.40	$54.40
Purchase #4	$178.81	6.301%	$190.0768	$190.08	$190.10	$190.10
Purchase #5	$211.85	4.365%	$221.0973	$221.10	$221.10	$221.10
Purchase #6	$129.40	9.621%	$141.8496	$141.85	$141.85	$141.80
Purchase #7	$71.29	3.249%	$73.6062	$73.61	$73.60	$73.60
7 purchase totals =	$949.62		$1,018.5831	$1,018.60	$1,018.60	$1,018.50