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	$115.77	13.301%	$131.1686	$131.17	$131.15	$131.20
Purchase #2	$110.65	3.230%	$114.224	$114.22	$114.20	$114.20
Purchase #3	$57.26	4.575%	$59.8796	$59.88	$59.90	$59.90
Purchase #4	$32.66	5.800%	$34.5543	$34.55	$34.55	$34.60
Purchase #5	$41.67	9.433%	$45.6007	$45.60	$45.60	$45.60
Purchase #6	$51.59	5.343%	$54.3465	$54.35	$54.35	$54.30
Purchase #7	$146.80	7.668%	$158.0566	$158.06	$158.05	$158.10
7 purchase totals =	$556.40		$597.8303	$597.83	$597.80	$597.90