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	$98.73	13.105%	$111.6686	$111.67	$111.65	$111.70
Purchase #2	$42.96	5.592%	$45.3623	$45.36	$45.35	$45.40
Purchase #3	$117.48	7.670%	$126.4907	$126.49	$126.50	$126.50
Purchase #4	$164.70	3.142%	$169.8749	$169.87	$169.85	$169.90
Purchase #5	$212.53	13.680%	$241.6041	$241.60	$241.60	$241.60
Purchase #6	$213.40	8.319%	$231.1527	$231.15	$231.15	$231.20
Purchase #7	$36.70	7.383%	$39.4096	$39.41	$39.40	$39.40
7 purchase totals =	$886.50		$965.5629	$965.55	$965.50	$965.70