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	$112.75	5.459%	$118.905	$118.91	$118.90	$118.90
Purchase #2	$122.93	3.798%	$127.5989	$127.60	$127.60	$127.60
Purchase #3	$92.35	12.658%	$104.0397	$104.04	$104.05	$104.00
Purchase #4	$12.81	13.557%	$14.5467	$14.55	$14.55	$14.50
Purchase #5	$91.85	5.488%	$96.8907	$96.89	$96.90	$96.90
Purchase #6	$43.29	8.361%	$46.9095	$46.91	$46.90	$46.90
Purchase #7	$239.61	4.409%	$250.1744	$250.17	$250.15	$250.20
7 purchase totals =	$715.59		$759.0649	$759.07	$759.05	$759.00