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	$157.69	8.443%	$171.0038	$171.00	$171.00	$171.00
Purchase #2	$81.62	10.638%	$90.3027	$90.30	$90.30	$90.30
Purchase #3	$35.50	5.850%	$37.5768	$37.58	$37.60	$37.60
Purchase #4	$115.55	5.804%	$122.2565	$122.26	$122.25	$122.30
Purchase #5	$94.47	5.214%	$99.3957	$99.40	$99.40	$99.40
Purchase #6	$11.30	10.162%	$12.4483	$12.45	$12.45	$12.40
Purchase #7	$143.87	7.320%	$154.4013	$154.40	$154.40	$154.40
7 purchase totals =	$640.00		$687.3851	$687.39	$687.40	$687.40