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	$64.90	11.416%	$72.309	$72.31	$72.30	$72.30
Purchase #2	$100.58	12.522%	$113.1746	$113.17	$113.15	$113.20
Purchase #3	$48.78	12.763%	$55.0058	$55.01	$55.00	$55.00
Purchase #4	$46.76	12.362%	$52.5405	$52.54	$52.55	$52.50
Purchase #5	$150.68	8.243%	$163.1006	$163.10	$163.10	$163.10
Purchase #6	$123.78	3.209%	$127.7521	$127.75	$127.75	$127.80
Purchase #7	$16.94	5.555%	$17.881	$17.88	$17.90	$17.90
7 purchase totals =	$552.42		$601.7636	$601.76	$601.75	$601.80