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	$38.88	11.215%	$43.2404	$43.24	$43.25	$43.20
Purchase #2	$250.34	10.839%	$277.4744	$277.47	$277.45	$277.50
Purchase #3	$130.86	10.502%	$144.6029	$144.60	$144.60	$144.60
Purchase #4	$49.62	12.664%	$55.9039	$55.90	$55.90	$55.90
Purchase #5	$109.73	10.813%	$121.5951	$121.60	$121.60	$121.60
Purchase #6	$162.64	5.421%	$171.4567	$171.46	$171.45	$171.50
Purchase #7	$43.96	5.333%	$46.3044	$46.30	$46.30	$46.30
7 purchase totals =	$786.03		$860.5778	$860.57	$860.55	$860.60