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	$42.31	3.509%	$43.7947	$43.79	$43.80	$43.80
Purchase #2	$240.62	6.736%	$256.8282	$256.83	$256.85	$256.80
Purchase #3	$10.58	12.498%	$11.9023	$11.90	$11.90	$11.90
Purchase #4	$187.30	4.731%	$196.1612	$196.16	$196.15	$196.20
Purchase #5	$186.41	3.535%	$192.9996	$193.00	$193.00	$193.00
Purchase #6	$40.69	5.327%	$42.8576	$42.86	$42.85	$42.90
Purchase #7	$136.83	13.447%	$155.2295	$155.23	$155.25	$155.20
7 purchase totals =	$844.74		$899.7731	$899.77	$899.80	$899.80