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	$250.79	7.253%	$268.9798	$268.98	$269.00	$269.00
Purchase #2	$191.66	13.714%	$217.9443	$217.94	$217.95	$217.90
Purchase #3	$190.76	13.796%	$217.0772	$217.08	$217.10	$217.10
Purchase #4	$205.45	12.397%	$230.9196	$230.92	$230.90	$230.90
Purchase #5	$6.47	4.617%	$6.7687	$6.77	$6.75	$6.80
Purchase #6	$10.52	3.569%	$10.8955	$10.90	$10.90	$10.90
Purchase #7	$70.86	10.490%	$78.2932	$78.29	$78.30	$78.30
7 purchase totals =	$926.51		$1,030.8783	$1,030.88	$1,030.90	$1,030.90