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	$14.92	8.725%	$16.2218	$16.22	$16.20	$16.20
Purchase #2	$80.77	10.460%	$89.2185	$89.22	$89.20	$89.20
Purchase #3	$239.31	4.302%	$249.6051	$249.61	$249.60	$249.60
Purchase #4	$119.35	6.390%	$126.9765	$126.98	$127.00	$127.00
Purchase #5	$49.41	10.270%	$54.4844	$54.48	$54.50	$54.50
Purchase #6	$42.93	6.624%	$45.7737	$45.77	$45.75	$45.80
Purchase #7	$227.71	5.155%	$239.4485	$239.45	$239.45	$239.40
7 purchase totals =	$774.40		$821.7285	$821.73	$821.70	$821.70