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	$140.67	8.688%	$152.8914	$152.89	$152.90	$152.90
Purchase #2	$127.74	11.232%	$142.0878	$142.09	$142.10	$142.10
Purchase #3	$151.42	6.210%	$160.8232	$160.82	$160.80	$160.80
Purchase #4	$39.27	4.655%	$41.098	$41.10	$41.10	$41.10
Purchase #5	$241.99	13.676%	$275.0846	$275.08	$275.10	$275.10
Purchase #6	$246.37	4.153%	$256.6017	$256.60	$256.60	$256.60
Purchase #7	$202.66	9.166%	$221.2358	$221.24	$221.25	$221.20
7 purchase totals =	$1,150.12		$1,249.8225	$1,249.82	$1,249.85	$1,249.80