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	$169.61	13.106%	$191.8391	$191.84	$191.85	$191.80
Purchase #2	$158.72	6.431%	$168.9273	$168.93	$168.95	$168.90
Purchase #3	$7.50	11.317%	$8.3488	$8.35	$8.35	$8.30
Purchase #4	$20.41	4.259%	$21.2793	$21.28	$21.30	$21.30
Purchase #5	$34.82	11.493%	$38.8219	$38.82	$38.80	$38.80
Purchase #6	$63.40	6.694%	$67.644	$67.64	$67.65	$67.60
Purchase #7	$85.88	11.308%	$95.5913	$95.59	$95.60	$95.60
7 purchase totals =	$540.34		$592.4517	$592.45	$592.50	$592.30