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	$51.96	10.378%	$57.3524	$57.35	$57.35	$57.40
Purchase #2	$246.41	6.510%	$262.4513	$262.45	$262.45	$262.50
Purchase #3	$157.47	7.203%	$168.8126	$168.81	$168.80	$168.80
Purchase #4	$127.92	4.146%	$133.2236	$133.22	$133.20	$133.20
Purchase #5	$244.25	11.117%	$271.4033	$271.40	$271.40	$271.40
Purchase #6	$53.84	10.324%	$59.3984	$59.40	$59.40	$59.40
Purchase #7	$40.37	13.166%	$45.6851	$45.69	$45.70	$45.70
7 purchase totals =	$922.22		$998.3267	$998.32	$998.30	$998.40