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	$76.29	8.428%	$82.7197	$82.72	$82.70	$82.70
Purchase #2	$58.29	4.739%	$61.0524	$61.05	$61.05	$61.10
Purchase #3	$31.54	12.410%	$35.4541	$35.45	$35.45	$35.50
Purchase #4	$78.92	4.649%	$82.589	$82.59	$82.60	$82.60
Purchase #5	$214.69	11.451%	$239.2742	$239.27	$239.25	$239.30
Purchase #6	$33.67	12.836%	$37.9919	$37.99	$38.00	$38.00
Purchase #7	$15.51	12.800%	$17.4953	$17.50	$17.50	$17.50
7 purchase totals =	$508.91		$556.5766	$556.57	$556.55	$556.70