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	$54.74	3.103%	$56.4386	$56.44	$56.45	$56.40
Purchase #2	$232.94	10.337%	$257.019	$257.02	$257.00	$257.00
Purchase #3	$42.37	12.395%	$47.6218	$47.62	$47.60	$47.60
Purchase #4	$107.50	3.798%	$111.5829	$111.58	$111.60	$111.60
Purchase #5	$210.86	5.810%	$223.111	$223.11	$223.10	$223.10
Purchase #6	$6.70	6.598%	$7.1421	$7.14	$7.15	$7.10
Purchase #7	$121.60	7.793%	$131.0763	$131.08	$131.10	$131.10
7 purchase totals =	$776.71		$833.9917	$833.99	$834.00	$833.90