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	$58.27	3.833%	$60.5035	$60.50	$60.50	$60.50
Purchase #2	$100.78	6.681%	$107.5131	$107.51	$107.50	$107.50
Purchase #3	$122.60	12.462%	$137.8784	$137.88	$137.90	$137.90
Purchase #4	$226.40	10.196%	$249.4837	$249.48	$249.50	$249.50
Purchase #5	$151.80	5.523%	$160.1839	$160.18	$160.20	$160.20
Purchase #6	$249.52	11.601%	$278.4668	$278.47	$278.45	$278.50
Purchase #7	$139.33	7.734%	$150.1058	$150.11	$150.10	$150.10
7 purchase totals =	$1,048.70		$1,144.1352	$1,144.13	$1,144.15	$1,144.20