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	$113.77	4.351%	$118.7201	$118.72	$118.70	$118.70
Purchase #2	$226.70	9.850%	$249.03	$249.03	$249.05	$249.00
Purchase #3	$25.86	9.326%	$28.2717	$28.27	$28.25	$28.30
Purchase #4	$95.36	5.768%	$100.8604	$100.86	$100.85	$100.90
Purchase #5	$95.54	8.484%	$103.6456	$103.65	$103.65	$103.60
Purchase #6	$65.54	4.367%	$68.4021	$68.40	$68.40	$68.40
Purchase #7	$85.98	7.680%	$92.5833	$92.58	$92.60	$92.60
7 purchase totals =	$708.75		$761.5132	$761.51	$761.50	$761.50