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	$41.33	9.167%	$45.1187	$45.12	$45.10	$45.10
Purchase #2	$208.32	11.128%	$231.5018	$231.50	$231.50	$231.50
Purchase #3	$136.30	13.330%	$154.4688	$154.47	$154.45	$154.50
Purchase #4	$88.70	5.260%	$93.3656	$93.37	$93.35	$93.40
Purchase #5	$93.51	10.536%	$103.3622	$103.36	$103.35	$103.40
Purchase #6	$151.33	6.121%	$160.5929	$160.59	$160.60	$160.60
Purchase #7	$119.32	4.342%	$124.5009	$124.50	$124.50	$124.50
7 purchase totals =	$838.81		$912.9109	$912.91	$912.85	$913.00