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	$97.66	11.466%	$108.8577	$108.86	$108.85	$108.90
Purchase #2	$142.40	11.176%	$158.3146	$158.31	$158.30	$158.30
Purchase #3	$28.47	12.153%	$31.93	$31.93	$31.95	$31.90
Purchase #4	$83.58	7.211%	$89.607	$89.61	$89.60	$89.60
Purchase #5	$142.33	11.189%	$158.2553	$158.26	$158.25	$158.30
Purchase #6	$92.51	8.787%	$100.6389	$100.64	$100.65	$100.60
Purchase #7	$9.29	5.435%	$9.7949	$9.79	$9.80	$9.80
7 purchase totals =	$596.24		$657.3984	$657.40	$657.40	$657.40