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	$138.92	4.724%	$145.4826	$145.48	$145.50	$145.50
Purchase #2	$40.81	11.348%	$45.4411	$45.44	$45.45	$45.40
Purchase #3	$142.55	4.247%	$148.6041	$148.60	$148.60	$148.60
Purchase #4	$31.40	13.346%	$35.5906	$35.59	$35.60	$35.60
Purchase #5	$248.96	12.150%	$279.2086	$279.21	$279.20	$279.20
Purchase #6	$83.32	3.861%	$86.537	$86.54	$86.55	$86.50
Purchase #7	$202.92	5.275%	$213.624	$213.62	$213.60	$213.60
7 purchase totals =	$888.88		$954.4880	$954.48	$954.50	$954.40