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	$96.29	6.302%	$102.3582	$102.36	$102.35	$102.40
Purchase #2	$198.30	6.334%	$210.8603	$210.86	$210.85	$210.90
Purchase #3	$149.91	13.107%	$169.5587	$169.56	$169.55	$169.60
Purchase #4	$75.36	9.111%	$82.226	$82.23	$82.25	$82.20
Purchase #5	$9.35	10.564%	$10.3377	$10.34	$10.35	$10.30
Purchase #6	$107.67	3.634%	$111.5827	$111.58	$111.60	$111.60
Purchase #7	$230.88	12.815%	$260.4673	$260.47	$260.45	$260.50
7 purchase totals =	$867.76		$947.3909	$947.40	$947.40	$947.50