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	$37.50	9.118%	$40.9193	$40.92	$40.90	$40.90
Purchase #2	$144.28	13.832%	$164.2368	$164.24	$164.25	$164.20
Purchase #3	$160.51	12.192%	$180.0794	$180.08	$180.10	$180.10
Purchase #4	$179.60	13.338%	$203.555	$203.56	$203.55	$203.60
Purchase #5	$92.84	13.546%	$105.4161	$105.42	$105.40	$105.40
Purchase #6	$94.75	7.365%	$101.7283	$101.73	$101.75	$101.70
Purchase #7	$78.37	3.226%	$80.8982	$80.90	$80.90	$80.90
7 purchase totals =	$787.85		$876.8331	$876.85	$876.85	$876.80