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	$113.28	12.863%	$127.8512	$127.85	$127.85	$127.90
Purchase #2	$94.58	8.396%	$102.5209	$102.52	$102.50	$102.50
Purchase #3	$90.34	13.183%	$102.2495	$102.25	$102.25	$102.20
Purchase #4	$132.96	8.441%	$144.1832	$144.18	$144.20	$144.20
Purchase #5	$71.57	5.617%	$75.5901	$75.59	$75.60	$75.60
Purchase #6	$95.27	13.180%	$107.8266	$107.83	$107.85	$107.80
Purchase #7	$68.64	4.314%	$71.6011	$71.60	$71.60	$71.60
7 purchase totals =	$666.64		$731.8226	$731.82	$731.85	$731.80