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	$101.47	3.104%	$104.6196	$104.62	$104.60	$104.60
Purchase #2	$185.47	4.189%	$193.2393	$193.24	$193.25	$193.20
Purchase #3	$86.25	4.686%	$90.2917	$90.29	$90.30	$90.30
Purchase #4	$139.47	11.507%	$155.5188	$155.52	$155.50	$155.50
Purchase #5	$110.61	10.616%	$122.3524	$122.35	$122.35	$122.40
Purchase #6	$99.58	3.300%	$102.8661	$102.87	$102.85	$102.90
Purchase #7	$15.98	11.545%	$17.8249	$17.82	$17.80	$17.80
7 purchase totals =	$738.83		$786.7128	$786.71	$786.65	$786.70