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	$156.40	6.412%	$166.4284	$166.43	$166.45	$166.40
Purchase #2	$20.42	7.111%	$21.8721	$21.87	$21.85	$21.90
Purchase #3	$169.59	3.349%	$175.2696	$175.27	$175.25	$175.30
Purchase #4	$19.31	6.236%	$20.5142	$20.51	$20.50	$20.50
Purchase #5	$112.83	6.258%	$119.8909	$119.89	$119.90	$119.90
Purchase #6	$89.71	12.543%	$100.9623	$100.96	$100.95	$101.00
Purchase #7	$76.86	6.288%	$81.693	$81.69	$81.70	$81.70
7 purchase totals =	$645.12		$686.6305	$686.62	$686.60	$686.70