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	$11.89	13.103%	$13.4479	$13.45	$13.45	$13.40
Purchase #2	$111.88	4.406%	$116.8094	$116.81	$116.80	$116.80
Purchase #3	$213.87	4.189%	$222.829	$222.83	$222.85	$222.80
Purchase #4	$116.67	4.378%	$121.7778	$121.78	$121.80	$121.80
Purchase #5	$118.86	10.630%	$131.4948	$131.49	$131.50	$131.50
Purchase #6	$178.47	6.151%	$189.4477	$189.45	$189.45	$189.40
Purchase #7	$27.62	4.302%	$28.8082	$28.81	$28.80	$28.80
7 purchase totals =	$779.26		$824.6148	$824.62	$824.65	$824.50