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	$216.47	12.111%	$242.6867	$242.69	$242.70	$242.70
Purchase #2	$108.73	13.138%	$123.0149	$123.01	$123.00	$123.00
Purchase #3	$148.30	5.444%	$156.3735	$156.37	$156.35	$156.40
Purchase #4	$86.51	11.189%	$96.1896	$96.19	$96.20	$96.20
Purchase #5	$207.75	11.440%	$231.5166	$231.52	$231.50	$231.50
Purchase #6	$43.43	11.642%	$48.4861	$48.49	$48.50	$48.50
Purchase #7	$65.88	11.445%	$73.42	$73.42	$73.40	$73.40
7 purchase totals =	$877.07		$971.6874	$971.69	$971.65	$971.70