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	$21.70	12.549%	$24.4231	$24.42	$24.40	$24.40
Purchase #2	$61.83	9.329%	$67.5981	$67.60	$67.60	$67.60
Purchase #3	$27.59	3.720%	$28.6163	$28.62	$28.60	$28.60
Purchase #4	$49.26	13.484%	$55.9022	$55.90	$55.90	$55.90
Purchase #5	$103.79	13.156%	$117.4446	$117.44	$117.45	$117.40
Purchase #6	$69.75	12.448%	$78.4325	$78.43	$78.45	$78.40
Purchase #7	$130.53	12.514%	$146.8645	$146.86	$146.85	$146.90
7 purchase totals =	$464.45		$519.2813	$519.27	$519.25	$519.20