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	$81.43	11.470%	$90.77	$90.77	$90.75	$90.80
Purchase #2	$144.79	6.775%	$154.5995	$154.60	$154.60	$154.60
Purchase #3	$136.69	8.465%	$148.2608	$148.26	$148.25	$148.30
Purchase #4	$82.89	11.511%	$92.4315	$92.43	$92.45	$92.40
Purchase #5	$95.38	4.287%	$99.4689	$99.47	$99.45	$99.50
Purchase #6	$186.93	13.678%	$212.4983	$212.50	$212.50	$212.50
Purchase #7	$121.26	8.697%	$131.806	$131.81	$131.80	$131.80
7 purchase totals =	$849.37		$929.8350	$929.84	$929.80	$929.90