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	$45.51	5.265%	$47.9061	$47.91	$47.90	$47.90
Purchase #2	$99.64	6.178%	$105.7958	$105.80	$105.80	$105.80
Purchase #3	$103.92	13.202%	$117.6395	$117.64	$117.65	$117.60
Purchase #4	$119.61	6.490%	$127.3727	$127.37	$127.35	$127.40
Purchase #5	$218.36	3.267%	$225.4938	$225.49	$225.50	$225.50
Purchase #6	$114.83	7.420%	$123.3504	$123.35	$123.35	$123.40
Purchase #7	$58.82	8.144%	$63.6103	$63.61	$63.60	$63.60
7 purchase totals =	$760.69		$811.1686	$811.17	$811.15	$811.20