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	$23.71	6.298%	$25.2033	$25.20	$25.20	$25.20
Purchase #2	$17.78	8.704%	$19.3276	$19.33	$19.35	$19.30
Purchase #3	$147.57	13.337%	$167.2514	$167.25	$167.25	$167.30
Purchase #4	$101.32	10.418%	$111.8755	$111.88	$111.90	$111.90
Purchase #5	$92.50	4.429%	$96.5968	$96.60	$96.60	$96.60
Purchase #6	$77.27	13.334%	$87.5732	$87.57	$87.55	$87.60
Purchase #7	$74.35	9.624%	$81.5054	$81.51	$81.50	$81.50
7 purchase totals =	$534.50		$589.3332	$589.34	$589.35	$589.40