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	$78.72	13.272%	$89.1677	$89.17	$89.15	$89.20
Purchase #2	$139.41	8.711%	$151.554	$151.55	$151.55	$151.60
Purchase #3	$154.38	3.501%	$159.7848	$159.78	$159.80	$159.80
Purchase #4	$43.44	8.105%	$46.9608	$46.96	$46.95	$47.00
Purchase #5	$192.95	5.868%	$204.2723	$204.27	$204.25	$204.30
Purchase #6	$12.41	7.804%	$13.3785	$13.38	$13.40	$13.40
Purchase #7	$126.68	3.811%	$131.5078	$131.51	$131.50	$131.50
7 purchase totals =	$747.99		$796.6259	$796.62	$796.60	$796.80