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	$37.80	10.735%	$41.8578	$41.86	$41.85	$41.90
Purchase #2	$114.78	7.217%	$123.0637	$123.06	$123.05	$123.10
Purchase #3	$155.90	12.308%	$175.0882	$175.09	$175.10	$175.10
Purchase #4	$49.32	5.611%	$52.0873	$52.09	$52.10	$52.10
Purchase #5	$85.70	5.627%	$90.5223	$90.52	$90.50	$90.50
Purchase #6	$98.91	9.821%	$108.624	$108.62	$108.60	$108.60
Purchase #7	$7.86	12.465%	$8.8397	$8.84	$8.85	$8.80
7 purchase totals =	$550.27		$600.0830	$600.08	$600.05	$600.10