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	$40.89	11.297%	$45.5093	$45.51	$45.50	$45.50
Purchase #2	$164.86	7.105%	$176.5733	$176.57	$176.55	$176.60
Purchase #3	$54.98	8.279%	$59.5318	$59.53	$59.55	$59.50
Purchase #4	$203.76	9.476%	$223.0683	$223.07	$223.05	$223.10
Purchase #5	$192.67	6.685%	$205.55	$205.55	$205.55	$205.60
Purchase #6	$39.31	9.844%	$43.1797	$43.18	$43.20	$43.20
Purchase #7	$202.75	11.397%	$225.8574	$225.86	$225.85	$225.90
7 purchase totals =	$899.22		$979.2698	$979.27	$979.25	$979.40