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	$127.86	6.414%	$136.0609	$136.06	$136.05	$136.10
Purchase #2	$101.97	9.104%	$111.2533	$111.25	$111.25	$111.30
Purchase #3	$89.29	9.770%	$98.0136	$98.01	$98.00	$98.00
Purchase #4	$50.88	10.423%	$56.1832	$56.18	$56.20	$56.20
Purchase #5	$143.66	7.470%	$154.3914	$154.39	$154.40	$154.40
Purchase #6	$123.61	5.118%	$129.9364	$129.94	$129.95	$129.90
Purchase #7	$206.43	13.387%	$234.0648	$234.06	$234.05	$234.10
7 purchase totals =	$843.70		$919.9036	$919.89	$919.90	$920.00