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	$16.80	8.689%	$18.2598	$18.26	$18.25	$18.30
Purchase #2	$173.56	10.761%	$192.2368	$192.24	$192.25	$192.20
Purchase #3	$38.82	12.308%	$43.598	$43.60	$43.60	$43.60
Purchase #4	$108.79	13.707%	$123.7018	$123.70	$123.70	$123.70
Purchase #5	$63.56	6.537%	$67.7149	$67.71	$67.70	$67.70
Purchase #6	$54.85	7.651%	$59.0466	$59.05	$59.05	$59.00
Purchase #7	$44.56	5.401%	$46.9667	$46.97	$46.95	$47.00
7 purchase totals =	$500.94		$551.5246	$551.53	$551.50	$551.50