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	$73.54	12.457%	$82.7009	$82.70	$82.70	$82.70
Purchase #2	$126.74	13.788%	$144.2149	$144.21	$144.20	$144.20
Purchase #3	$34.60	5.336%	$36.4463	$36.45	$36.45	$36.40
Purchase #4	$143.46	13.684%	$163.0911	$163.09	$163.10	$163.10
Purchase #5	$115.32	5.356%	$121.4965	$121.50	$121.50	$121.50
Purchase #6	$59.82	3.443%	$61.8796	$61.88	$61.90	$61.90
Purchase #7	$80.47	12.606%	$90.614	$90.61	$90.60	$90.60
7 purchase totals =	$633.95		$700.4433	$700.44	$700.45	$700.40