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	$30.51	3.608%	$31.6108	$31.61	$31.60	$31.60
Purchase #2	$28.43	9.720%	$31.1934	$31.19	$31.20	$31.20
Purchase #3	$96.66	10.286%	$106.6024	$106.60	$106.60	$106.60
Purchase #4	$81.74	13.265%	$92.5828	$92.58	$92.60	$92.60
Purchase #5	$132.95	10.308%	$146.6545	$146.65	$146.65	$146.70
Purchase #6	$6.29	12.731%	$7.0908	$7.09	$7.10	$7.10
Purchase #7	$153.83	11.484%	$171.4958	$171.50	$171.50	$171.50
7 purchase totals =	$530.41		$587.2305	$587.22	$587.25	$587.30