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	$37.75	8.339%	$40.898	$40.90	$40.90	$40.90
Purchase #2	$13.88	11.514%	$15.4781	$15.48	$15.50	$15.50
Purchase #3	$116.92	5.568%	$123.4301	$123.43	$123.45	$123.40
Purchase #4	$86.60	5.631%	$91.4764	$91.48	$91.50	$91.50
Purchase #5	$202.93	11.498%	$226.2629	$226.26	$226.25	$226.30
Purchase #6	$33.70	5.295%	$35.4844	$35.48	$35.50	$35.50
Purchase #7	$9.88	5.525%	$10.4259	$10.43	$10.45	$10.40
7 purchase totals =	$501.66		$543.4558	$543.46	$543.55	$543.50