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	$35.73	13.659%	$40.6104	$40.61	$40.60	$40.60
Purchase #2	$199.81	5.641%	$211.0813	$211.08	$211.10	$211.10
Purchase #3	$151.51	8.371%	$164.1929	$164.19	$164.20	$164.20
Purchase #4	$119.92	8.527%	$130.1456	$130.15	$130.15	$130.10
Purchase #5	$111.91	4.112%	$116.5117	$116.51	$116.50	$116.50
Purchase #6	$127.42	6.543%	$135.7571	$135.76	$135.75	$135.80
Purchase #7	$107.41	4.510%	$112.2542	$112.25	$112.25	$112.30
7 purchase totals =	$853.71		$910.5532	$910.55	$910.55	$910.60