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	$38.74	9.621%	$42.4672	$42.47	$42.45	$42.50
Purchase #2	$52.50	6.872%	$56.1078	$56.11	$56.10	$56.10
Purchase #3	$209.58	3.766%	$217.4728	$217.47	$217.45	$217.50
Purchase #4	$130.78	12.627%	$147.2936	$147.29	$147.30	$147.30
Purchase #5	$181.42	10.310%	$200.1244	$200.12	$200.10	$200.10
Purchase #6	$157.84	7.607%	$169.8469	$169.85	$169.85	$169.80
Purchase #7	$224.94	7.492%	$241.7925	$241.79	$241.80	$241.80
7 purchase totals =	$995.80		$1,075.1052	$1,075.10	$1,075.05	$1,075.10