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	$153.59	7.160%	$164.587	$164.59	$164.60	$164.60
Purchase #2	$163.91	11.231%	$182.3187	$182.32	$182.30	$182.30
Purchase #3	$89.37	11.341%	$99.5055	$99.51	$99.50	$99.50
Purchase #4	$112.42	13.531%	$127.6316	$127.63	$127.65	$127.60
Purchase #5	$125.38	12.583%	$141.1566	$141.16	$141.15	$141.20
Purchase #6	$76.51	12.459%	$86.0424	$86.04	$86.05	$86.00
Purchase #7	$35.60	7.421%	$38.2419	$38.24	$38.25	$38.20
7 purchase totals =	$756.78		$839.4837	$839.49	$839.50	$839.40