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	$80.61	11.179%	$89.6214	$89.62	$89.60	$89.60
Purchase #2	$176.38	5.169%	$185.4971	$185.50	$185.50	$185.50
Purchase #3	$123.75	10.477%	$136.7153	$136.72	$136.70	$136.70
Purchase #4	$174.67	5.193%	$183.7406	$183.74	$183.75	$183.70
Purchase #5	$250.76	12.739%	$282.7043	$282.70	$282.70	$282.70
Purchase #6	$161.72	10.465%	$178.644	$178.64	$178.65	$178.60
Purchase #7	$240.97	7.674%	$259.462	$259.46	$259.45	$259.50
7 purchase totals =	$1,208.86		$1,316.3847	$1,316.38	$1,316.35	$1,316.30