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	$94.40	10.375%	$104.194	$104.19	$104.20	$104.20
Purchase #2	$105.43	5.577%	$111.3098	$111.31	$111.30	$111.30
Purchase #3	$61.43	8.844%	$66.8629	$66.86	$66.85	$66.90
Purchase #4	$237.66	7.158%	$254.6717	$254.67	$254.65	$254.70
Purchase #5	$112.96	6.268%	$120.0403	$120.04	$120.05	$120.00
Purchase #6	$90.58	7.253%	$97.1498	$97.15	$97.15	$97.10
Purchase #7	$40.75	11.365%	$45.3812	$45.38	$45.40	$45.40
7 purchase totals =	$743.21		$799.6097	$799.60	$799.60	$799.60