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	$124.58	3.300%	$128.6911	$128.69	$128.70	$128.70
Purchase #2	$101.27	5.709%	$107.0515	$107.05	$107.05	$107.10
Purchase #3	$173.87	9.537%	$190.452	$190.45	$190.45	$190.50
Purchase #4	$116.60	4.230%	$121.5322	$121.53	$121.55	$121.50
Purchase #5	$82.73	8.316%	$89.6098	$89.61	$89.60	$89.60
Purchase #6	$96.46	8.455%	$104.6157	$104.62	$104.60	$104.60
Purchase #7	$69.49	4.138%	$72.3655	$72.37	$72.35	$72.40
7 purchase totals =	$765.00		$814.3178	$814.32	$814.30	$814.40