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	$136.77	13.349%	$155.0274	$155.03	$155.05	$155.00
Purchase #2	$76.76	11.714%	$85.7517	$85.75	$85.75	$85.80
Purchase #3	$108.53	8.563%	$117.8234	$117.82	$117.80	$117.80
Purchase #4	$32.65	5.180%	$34.3413	$34.34	$34.35	$34.30
Purchase #5	$39.52	9.526%	$43.2847	$43.28	$43.30	$43.30
Purchase #6	$53.67	3.447%	$55.52	$55.52	$55.50	$55.50
Purchase #7	$25.93	4.645%	$27.1344	$27.13	$27.15	$27.10
7 purchase totals =	$473.83		$518.8829	$518.87	$518.90	$518.80