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	$84.58	5.545%	$89.27	$89.27	$89.25	$89.30
Purchase #2	$40.68	4.266%	$42.4154	$42.42	$42.40	$42.40
Purchase #3	$31.50	9.477%	$34.4853	$34.49	$34.50	$34.50
Purchase #4	$167.52	3.271%	$172.9996	$173.00	$173.00	$173.00
Purchase #5	$151.57	11.129%	$168.4382	$168.44	$168.45	$168.40
Purchase #6	$143.37	13.302%	$162.4411	$162.44	$162.45	$162.40
Purchase #7	$206.82	13.710%	$235.175	$235.18	$235.20	$235.20
7 purchase totals =	$826.04		$905.2246	$905.24	$905.25	$905.20