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	$66.86	5.446%	$70.5012	$70.50	$70.50	$70.50
Purchase #2	$143.77	7.625%	$154.7325	$154.73	$154.75	$154.70
Purchase #3	$55.60	4.409%	$58.0514	$58.05	$58.05	$58.10
Purchase #4	$64.52	11.821%	$72.1469	$72.15	$72.15	$72.10
Purchase #5	$151.52	3.561%	$156.9156	$156.92	$156.90	$156.90
Purchase #6	$52.99	7.283%	$56.8493	$56.85	$56.85	$56.80
Purchase #7	$158.55	8.105%	$171.4005	$171.40	$171.40	$171.40
7 purchase totals =	$693.81		$740.5974	$740.60	$740.60	$740.50