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	$37.38	8.630%	$40.6059	$40.61	$40.60	$40.60
Purchase #2	$239.52	12.495%	$269.448	$269.45	$269.45	$269.40
Purchase #3	$11.41	7.543%	$12.2707	$12.27	$12.25	$12.30
Purchase #4	$80.57	10.761%	$89.2401	$89.24	$89.25	$89.20
Purchase #5	$12.69	6.135%	$13.4685	$13.47	$13.45	$13.50
Purchase #6	$229.85	12.118%	$257.7032	$257.70	$257.70	$257.70
Purchase #7	$224.46	10.810%	$248.7241	$248.72	$248.70	$248.70
7 purchase totals =	$835.88		$931.4605	$931.46	$931.40	$931.40