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	$21.65	5.221%	$22.7803	$22.78	$22.80	$22.80
Purchase #2	$102.96	8.442%	$111.6519	$111.65	$111.65	$111.70
Purchase #3	$64.47	4.355%	$67.2777	$67.28	$67.30	$67.30
Purchase #4	$238.56	4.655%	$249.665	$249.67	$249.65	$249.70
Purchase #5	$159.57	5.722%	$168.7006	$168.70	$168.70	$168.70
Purchase #6	$228.87	13.207%	$259.0969	$259.10	$259.10	$259.10
Purchase #7	$181.85	4.700%	$190.397	$190.40	$190.40	$190.40
7 purchase totals =	$997.93		$1,069.5694	$1,069.58	$1,069.60	$1,069.70