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	$53.65	11.654%	$59.9024	$59.90	$59.90	$59.90
Purchase #2	$150.33	10.479%	$166.0831	$166.08	$166.10	$166.10
Purchase #3	$45.76	12.528%	$51.4928	$51.49	$51.50	$51.50
Purchase #4	$128.80	3.856%	$133.7665	$133.77	$133.75	$133.80
Purchase #5	$179.28	10.732%	$198.5203	$198.52	$198.50	$198.50
Purchase #6	$20.61	6.514%	$21.9525	$21.95	$21.95	$22.00
Purchase #7	$18.50	10.536%	$20.4492	$20.45	$20.45	$20.40
7 purchase totals =	$596.93		$652.1668	$652.16	$652.15	$652.20