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	$41.91	9.501%	$45.8919	$45.89	$45.90	$45.90
Purchase #2	$118.31	13.699%	$134.5173	$134.52	$134.50	$134.50
Purchase #3	$16.43	12.271%	$18.4461	$18.45	$18.45	$18.40
Purchase #4	$185.72	8.532%	$201.5656	$201.57	$201.55	$201.60
Purchase #5	$164.78	4.610%	$172.3764	$172.38	$172.40	$172.40
Purchase #6	$160.60	10.536%	$177.5208	$177.52	$177.50	$177.50
Purchase #7	$103.77	4.615%	$108.559	$108.56	$108.55	$108.60
7 purchase totals =	$791.52		$858.8771	$858.89	$858.85	$858.90