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	$17.94	12.245%	$20.1368	$20.14	$20.15	$20.10
Purchase #2	$155.32	3.566%	$160.8587	$160.86	$160.85	$160.90
Purchase #3	$56.58	5.836%	$59.882	$59.88	$59.90	$59.90
Purchase #4	$10.42	7.789%	$11.2316	$11.23	$11.25	$11.20
Purchase #5	$126.30	5.124%	$132.7716	$132.77	$132.75	$132.80
Purchase #6	$246.46	13.824%	$280.5306	$280.53	$280.55	$280.50
Purchase #7	$119.43	7.311%	$128.1615	$128.16	$128.15	$128.20
7 purchase totals =	$732.45		$793.5728	$793.57	$793.60	$793.60