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	$39.28	9.450%	$42.992	$42.99	$43.00	$43.00
Purchase #2	$100.81	12.798%	$113.7117	$113.71	$113.70	$113.70
Purchase #3	$70.83	13.120%	$80.1229	$80.12	$80.10	$80.10
Purchase #4	$188.88	5.109%	$198.5299	$198.53	$198.55	$198.50
Purchase #5	$52.72	3.216%	$54.4155	$54.42	$54.40	$54.40
Purchase #6	$242.77	5.697%	$256.6006	$256.60	$256.60	$256.60
Purchase #7	$196.72	10.340%	$217.0608	$217.06	$217.05	$217.10
7 purchase totals =	$892.01		$963.4334	$963.43	$963.40	$963.40