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	$38.63	10.297%	$42.6077	$42.61	$42.60	$42.60
Purchase #2	$96.87	13.467%	$109.9155	$109.92	$109.90	$109.90
Purchase #3	$45.87	11.108%	$50.9652	$50.97	$50.95	$51.00
Purchase #4	$31.53	4.151%	$32.8388	$32.84	$32.85	$32.80
Purchase #5	$136.64	10.174%	$150.5418	$150.54	$150.55	$150.50
Purchase #6	$160.26	10.405%	$176.9351	$176.94	$176.95	$176.90
Purchase #7	$22.27	3.806%	$23.1176	$23.12	$23.10	$23.10
7 purchase totals =	$532.07		$586.9217	$586.94	$586.90	$586.80