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	$229.39	12.846%	$258.8574	$258.86	$258.85	$258.90
Purchase #2	$24.47	12.665%	$27.5691	$27.57	$27.55	$27.60
Purchase #3	$240.72	12.836%	$271.6188	$271.62	$271.60	$271.60
Purchase #4	$100.69	8.678%	$109.4279	$109.43	$109.45	$109.40
Purchase #5	$28.96	10.541%	$32.0127	$32.01	$32.00	$32.00
Purchase #6	$217.38	3.316%	$224.5883	$224.59	$224.60	$224.60
Purchase #7	$186.83	8.704%	$203.0917	$203.09	$203.10	$203.10
7 purchase totals =	$1,028.44		$1,127.1659	$1,127.17	$1,127.15	$1,127.20