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	$74.87	11.798%	$83.7032	$83.70	$83.70	$83.70
Purchase #2	$92.78	10.782%	$102.7835	$102.78	$102.80	$102.80
Purchase #3	$137.81	4.865%	$144.5145	$144.51	$144.50	$144.50
Purchase #4	$107.94	12.360%	$121.2814	$121.28	$121.30	$121.30
Purchase #5	$18.45	12.540%	$20.7636	$20.76	$20.75	$20.80
Purchase #6	$225.96	5.720%	$238.8849	$238.88	$238.90	$238.90
Purchase #7	$54.96	4.839%	$57.6195	$57.62	$57.60	$57.60
7 purchase totals =	$712.77		$769.5506	$769.53	$769.55	$769.60