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	$112.52	13.349%	$127.5403	$127.54	$127.55	$127.50
Purchase #2	$39.66	10.202%	$43.7061	$43.71	$43.70	$43.70
Purchase #3	$22.46	6.601%	$23.9426	$23.94	$23.95	$23.90
Purchase #4	$108.41	13.707%	$123.2698	$123.27	$123.25	$123.30
Purchase #5	$103.32	8.864%	$112.4783	$112.48	$112.50	$112.50
Purchase #6	$100.96	6.143%	$107.162	$107.16	$107.15	$107.20
Purchase #7	$24.36	5.860%	$25.7875	$25.79	$25.80	$25.80
7 purchase totals =	$511.69		$563.8866	$563.89	$563.90	$563.90