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	$34.52	10.341%	$38.0897	$38.09	$38.10	$38.10
Purchase #2	$186.34	6.760%	$198.9366	$198.94	$198.95	$198.90
Purchase #3	$86.29	8.365%	$93.5082	$93.51	$93.50	$93.50
Purchase #4	$46.25	11.270%	$51.4624	$51.46	$51.45	$51.50
Purchase #5	$75.70	12.858%	$85.4335	$85.43	$85.45	$85.40
Purchase #6	$12.56	8.162%	$13.5851	$13.59	$13.60	$13.60
Purchase #7	$59.53	8.824%	$64.7829	$64.78	$64.80	$64.80
7 purchase totals =	$501.19		$545.7984	$545.80	$545.85	$545.80