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	$70.41	10.607%	$77.8784	$77.88	$77.90	$77.90
Purchase #2	$109.95	8.471%	$119.2639	$119.26	$119.25	$119.30
Purchase #3	$121.69	7.873%	$131.2707	$131.27	$131.25	$131.30
Purchase #4	$164.39	8.707%	$178.7034	$178.70	$178.70	$178.70
Purchase #5	$223.44	3.141%	$230.4583	$230.46	$230.45	$230.50
Purchase #6	$40.76	3.810%	$42.313	$42.31	$42.30	$42.30
Purchase #7	$86.60	4.617%	$90.5983	$90.60	$90.60	$90.60
7 purchase totals =	$817.24		$870.4860	$870.48	$870.45	$870.60