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	$45.37	9.750%	$49.7936	$49.79	$49.80	$49.80
Purchase #2	$109.54	7.407%	$117.6536	$117.65	$117.65	$117.70
Purchase #3	$169.42	7.127%	$181.4946	$181.49	$181.50	$181.50
Purchase #4	$78.37	3.465%	$81.0855	$81.09	$81.10	$81.10
Purchase #5	$170.62	8.382%	$184.9214	$184.92	$184.90	$184.90
Purchase #6	$113.86	11.782%	$127.275	$127.28	$127.30	$127.30
Purchase #7	$54.44	9.612%	$59.6728	$59.67	$59.65	$59.70
7 purchase totals =	$741.62		$801.8965	$801.89	$801.90	$802.00