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	$134.74	3.555%	$139.53	$139.53	$139.55	$139.50
Purchase #2	$19.45	12.660%	$21.9124	$21.91	$21.90	$21.90
Purchase #3	$56.46	4.589%	$59.0509	$59.05	$59.05	$59.10
Purchase #4	$43.51	4.317%	$45.3883	$45.39	$45.40	$45.40
Purchase #5	$112.85	4.689%	$118.1415	$118.14	$118.15	$118.10
Purchase #6	$226.30	4.440%	$236.3477	$236.35	$236.35	$236.30
Purchase #7	$132.93	7.517%	$142.9223	$142.92	$142.90	$142.90
7 purchase totals =	$726.24		$763.2931	$763.29	$763.30	$763.20