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	$156.27	5.479%	$164.832	$164.83	$164.85	$164.80
Purchase #2	$243.76	4.300%	$254.2417	$254.24	$254.25	$254.20
Purchase #3	$188.57	10.731%	$208.8054	$208.81	$208.80	$208.80
Purchase #4	$144.46	11.203%	$160.6439	$160.64	$160.65	$160.60
Purchase #5	$47.87	7.505%	$51.4626	$51.46	$51.45	$51.50
Purchase #6	$238.86	6.790%	$255.0786	$255.08	$255.10	$255.10
Purchase #7	$73.64	3.663%	$76.3374	$76.34	$76.35	$76.30
7 purchase totals =	$1,093.43		$1,171.4016	$1,171.40	$1,171.45	$1,171.30