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	$80.47	10.704%	$89.0835	$89.08	$89.10	$89.10
Purchase #2	$133.81	3.337%	$138.2752	$138.28	$138.30	$138.30
Purchase #3	$11.65	11.501%	$12.9899	$12.99	$13.00	$13.00
Purchase #4	$43.54	6.747%	$46.4776	$46.48	$46.50	$46.50
Purchase #5	$19.52	12.467%	$21.9536	$21.95	$21.95	$22.00
Purchase #6	$116.45	13.285%	$131.9204	$131.92	$131.90	$131.90
Purchase #7	$229.69	10.309%	$253.3687	$253.37	$253.35	$253.40
7 purchase totals =	$635.13		$694.0689	$694.07	$694.10	$694.20