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	$101.39	8.670%	$110.1805	$110.18	$110.20	$110.20
Purchase #2	$78.45	5.409%	$82.6934	$82.69	$82.70	$82.70
Purchase #3	$74.97	9.546%	$82.1266	$82.13	$82.15	$82.10
Purchase #4	$42.64	7.190%	$45.7058	$45.71	$45.70	$45.70
Purchase #5	$198.64	8.495%	$215.5145	$215.51	$215.50	$215.50
Purchase #6	$237.68	7.847%	$256.3307	$256.33	$256.35	$256.30
Purchase #7	$72.76	6.534%	$77.5141	$77.51	$77.50	$77.50
7 purchase totals =	$806.53		$870.0656	$870.06	$870.10	$870.00