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	$67.96	6.761%	$72.5548	$72.55	$72.55	$72.60
Purchase #2	$92.89	13.119%	$105.0762	$105.08	$105.10	$105.10
Purchase #3	$177.56	11.671%	$198.283	$198.28	$198.30	$198.30
Purchase #4	$166.71	6.686%	$177.8562	$177.86	$177.85	$177.90
Purchase #5	$125.95	9.127%	$137.4455	$137.45	$137.45	$137.40
Purchase #6	$102.66	5.582%	$108.3905	$108.39	$108.40	$108.40
Purchase #7	$20.27	3.309%	$20.9407	$20.94	$20.95	$20.90
7 purchase totals =	$754.00		$820.5469	$820.55	$820.60	$820.60