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	$43.41	4.816%	$45.5006	$45.50	$45.50	$45.50
Purchase #2	$162.72	6.294%	$172.9616	$172.96	$172.95	$173.00
Purchase #3	$72.63	8.458%	$78.773	$78.77	$78.75	$78.80
Purchase #4	$163.65	12.700%	$184.4336	$184.43	$184.45	$184.40
Purchase #5	$138.95	13.413%	$157.5874	$157.59	$157.60	$157.60
Purchase #6	$248.26	10.132%	$273.4137	$273.41	$273.40	$273.40
Purchase #7	$33.28	9.711%	$36.5118	$36.51	$36.50	$36.50
7 purchase totals =	$862.90		$949.1817	$949.17	$949.15	$949.20