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	$214.78	3.189%	$221.6293	$221.63	$221.65	$221.60
Purchase #2	$102.55	9.406%	$112.1959	$112.20	$112.20	$112.20
Purchase #3	$228.42	3.227%	$235.7911	$235.79	$235.80	$235.80
Purchase #4	$26.82	7.461%	$28.821	$28.82	$28.80	$28.80
Purchase #5	$185.43	5.797%	$196.1794	$196.18	$196.20	$196.20
Purchase #6	$60.28	8.449%	$65.3731	$65.37	$65.35	$65.40
Purchase #7	$126.97	12.564%	$142.9225	$142.92	$142.90	$142.90
7 purchase totals =	$945.25		$1,002.9123	$1,002.91	$1,002.90	$1,002.90