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	$166.34	13.822%	$189.3315	$189.33	$189.35	$189.30
Purchase #2	$106.72	7.453%	$114.6738	$114.67	$114.65	$114.70
Purchase #3	$138.36	4.679%	$144.8339	$144.83	$144.85	$144.80
Purchase #4	$31.62	5.210%	$33.2674	$33.27	$33.25	$33.30
Purchase #5	$48.91	9.583%	$53.597	$53.60	$53.60	$53.60
Purchase #6	$53.90	10.421%	$59.5169	$59.52	$59.50	$59.50
Purchase #7	$41.81	4.484%	$43.6848	$43.68	$43.70	$43.70
7 purchase totals =	$587.66		$638.9053	$638.90	$638.90	$638.90