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	$225.55	10.594%	$249.4448	$249.44	$249.45	$249.40
Purchase #2	$43.43	5.645%	$45.8816	$45.88	$45.90	$45.90
Purchase #3	$197.46	6.543%	$210.3798	$210.38	$210.40	$210.40
Purchase #4	$8.44	5.230%	$8.8814	$8.88	$8.90	$8.90
Purchase #5	$105.64	5.389%	$111.3329	$111.33	$111.35	$111.30
Purchase #6	$27.98	12.282%	$31.4165	$31.42	$31.40	$31.40
Purchase #7	$100.36	3.226%	$103.5976	$103.60	$103.60	$103.60
7 purchase totals =	$708.86		$760.9346	$760.93	$761.00	$760.90