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	$81.30	11.170%	$90.3812	$90.38	$90.40	$90.40
Purchase #2	$237.76	8.428%	$257.7984	$257.80	$257.80	$257.80
Purchase #3	$109.54	9.178%	$119.5936	$119.59	$119.60	$119.60
Purchase #4	$217.75	5.396%	$229.4998	$229.50	$229.50	$229.50
Purchase #5	$171.46	6.456%	$182.5295	$182.53	$182.55	$182.50
Purchase #6	$153.65	4.363%	$160.3537	$160.35	$160.35	$160.40
Purchase #7	$31.94	8.346%	$34.6057	$34.61	$34.60	$34.60
7 purchase totals =	$1,003.40		$1,074.7619	$1,074.76	$1,074.80	$1,074.80