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	$238.41	11.649%	$266.1824	$266.18	$266.20	$266.20
Purchase #2	$34.86	6.191%	$37.0182	$37.02	$37.00	$37.00
Purchase #3	$159.36	11.854%	$178.2505	$178.25	$178.25	$178.30
Purchase #4	$225.45	6.572%	$240.2666	$240.27	$240.25	$240.30
Purchase #5	$38.57	11.142%	$42.8675	$42.87	$42.85	$42.90
Purchase #6	$199.43	10.508%	$220.3861	$220.39	$220.40	$220.40
Purchase #7	$51.50	13.665%	$58.5375	$58.54	$58.55	$58.50
7 purchase totals =	$947.58		$1,043.5088	$1,043.52	$1,043.50	$1,043.60