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	$26.91	11.654%	$30.0461	$30.05	$30.05	$30.00
Purchase #2	$117.39	5.532%	$123.884	$123.88	$123.90	$123.90
Purchase #3	$128.31	10.724%	$142.07	$142.07	$142.05	$142.10
Purchase #4	$77.83	6.133%	$82.6033	$82.60	$82.60	$82.60
Purchase #5	$236.69	12.773%	$266.9224	$266.92	$266.90	$266.90
Purchase #6	$81.25	13.394%	$92.1326	$92.13	$92.15	$92.10
Purchase #7	$56.90	9.691%	$62.4142	$62.41	$62.40	$62.40
7 purchase totals =	$725.28		$800.0726	$800.06	$800.05	$800.00