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	$210.51	9.849%	$231.2431	$231.24	$231.25	$231.20
Purchase #2	$35.93	11.718%	$40.1403	$40.14	$40.15	$40.10
Purchase #3	$71.80	10.457%	$79.3081	$79.31	$79.30	$79.30
Purchase #4	$132.43	9.113%	$144.4983	$144.50	$144.50	$144.50
Purchase #5	$72.95	4.644%	$76.3378	$76.34	$76.35	$76.30
Purchase #6	$120.96	5.302%	$127.3733	$127.37	$127.35	$127.40
Purchase #7	$119.41	3.357%	$123.4186	$123.42	$123.40	$123.40
7 purchase totals =	$763.99		$822.3195	$822.32	$822.30	$822.20