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	$111.55	9.451%	$122.0926	$122.09	$122.10	$122.10
Purchase #2	$234.57	3.484%	$242.7424	$242.74	$242.75	$242.70
Purchase #3	$72.74	7.628%	$78.2886	$78.29	$78.30	$78.30
Purchase #4	$91.47	5.599%	$96.5914	$96.59	$96.60	$96.60
Purchase #5	$19.64	9.575%	$21.5205	$21.52	$21.50	$21.50
Purchase #6	$123.32	6.819%	$131.7292	$131.73	$131.75	$131.70
Purchase #7	$72.48	4.719%	$75.9003	$75.90	$75.90	$75.90
7 purchase totals =	$725.77		$768.8650	$768.86	$768.90	$768.80