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	$245.97	8.320%	$266.4347	$266.43	$266.45	$266.40
Purchase #2	$203.45	6.610%	$216.898	$216.90	$216.90	$216.90
Purchase #3	$203.26	10.105%	$223.7994	$223.80	$223.80	$223.80
Purchase #4	$184.57	5.803%	$195.2806	$195.28	$195.30	$195.30
Purchase #5	$72.80	9.322%	$79.5864	$79.59	$79.60	$79.60
Purchase #6	$109.35	13.132%	$123.7098	$123.71	$123.70	$123.70
Purchase #7	$58.32	4.808%	$61.124	$61.12	$61.10	$61.10
7 purchase totals =	$1,077.72		$1,166.8329	$1,166.83	$1,166.85	$1,166.80