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	$109.34	8.333%	$118.4513	$118.45	$118.45	$118.50
Purchase #2	$8.61	10.446%	$9.5094	$9.51	$9.50	$9.50
Purchase #3	$143.98	4.727%	$150.7859	$150.79	$150.80	$150.80
Purchase #4	$45.86	7.618%	$49.3536	$49.35	$49.35	$49.40
Purchase #5	$86.88	4.123%	$90.4621	$90.46	$90.45	$90.50
Purchase #6	$43.25	12.573%	$48.6878	$48.69	$48.70	$48.70
Purchase #7	$116.97	10.672%	$129.453	$129.45	$129.45	$129.50
7 purchase totals =	$554.89		$596.7031	$596.70	$596.70	$596.90