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	$129.57	5.676%	$136.9244	$136.92	$136.90	$136.90
Purchase #2	$231.95	10.307%	$255.8571	$255.86	$255.85	$255.90
Purchase #3	$135.41	7.590%	$145.6876	$145.69	$145.70	$145.70
Purchase #4	$174.59	12.709%	$196.7786	$196.78	$196.80	$196.80
Purchase #5	$248.62	11.195%	$276.453	$276.45	$276.45	$276.50
Purchase #6	$155.61	10.711%	$172.2774	$172.28	$172.30	$172.30
Purchase #7	$204.82	3.431%	$211.8474	$211.85	$211.85	$211.80
7 purchase totals =	$1,280.57		$1,395.8255	$1,395.83	$1,395.85	$1,395.90