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	$64.36	13.336%	$72.943	$72.94	$72.95	$72.90
Purchase #2	$228.32	10.580%	$252.4763	$252.48	$252.50	$252.50
Purchase #3	$54.81	4.691%	$57.3811	$57.38	$57.40	$57.40
Purchase #4	$183.28	4.546%	$191.6119	$191.61	$191.60	$191.60
Purchase #5	$200.26	3.306%	$206.8806	$206.88	$206.90	$206.90
Purchase #6	$126.43	12.605%	$142.3665	$142.37	$142.35	$142.40
Purchase #7	$142.77	10.181%	$157.3054	$157.31	$157.30	$157.30
7 purchase totals =	$1,000.23		$1,080.9648	$1,080.97	$1,081.00	$1,081.00