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	$48.34	6.113%	$51.295	$51.30	$51.30	$51.30
Purchase #2	$59.33	6.244%	$63.0346	$63.03	$63.05	$63.00
Purchase #3	$136.89	5.258%	$144.0877	$144.09	$144.10	$144.10
Purchase #4	$41.71	10.321%	$46.0149	$46.01	$46.00	$46.00
Purchase #5	$142.95	5.198%	$150.3805	$150.38	$150.40	$150.40
Purchase #6	$110.79	12.481%	$124.6177	$124.62	$124.60	$124.60
Purchase #7	$111.29	11.290%	$123.8546	$123.85	$123.85	$123.90
7 purchase totals =	$651.30		$703.2850	$703.28	$703.30	$703.30