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	$226.28	3.256%	$233.6477	$233.65	$233.65	$233.60
Purchase #2	$38.32	6.416%	$40.7786	$40.78	$40.80	$40.80
Purchase #3	$155.57	7.770%	$167.6578	$167.66	$167.65	$167.70
Purchase #4	$41.62	10.211%	$45.8698	$45.87	$45.85	$45.90
Purchase #5	$145.37	10.634%	$160.8286	$160.83	$160.85	$160.80
Purchase #6	$84.38	7.691%	$90.8697	$90.87	$90.85	$90.90
Purchase #7	$46.29	9.815%	$50.8334	$50.83	$50.85	$50.80
7 purchase totals =	$737.83		$790.4856	$790.49	$790.50	$790.50