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	$9.91	5.512%	$10.4562	$10.46	$10.45	$10.50
Purchase #2	$136.55	11.358%	$152.0593	$152.06	$152.05	$152.10
Purchase #3	$163.62	3.683%	$169.6461	$169.65	$169.65	$169.60
Purchase #4	$117.51	12.281%	$131.9414	$131.94	$131.95	$131.90
Purchase #5	$122.32	4.297%	$127.5761	$127.58	$127.60	$127.60
Purchase #6	$6.41	11.355%	$7.1379	$7.14	$7.15	$7.10
Purchase #7	$57.35	9.253%	$62.6566	$62.66	$62.65	$62.70
7 purchase totals =	$613.67		$661.4736	$661.49	$661.50	$661.50