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	$15.98	5.630%	$16.8797	$16.88	$16.90	$16.90
Purchase #2	$70.98	10.803%	$78.648	$78.65	$78.65	$78.60
Purchase #3	$51.80	6.432%	$55.1318	$55.13	$55.15	$55.10
Purchase #4	$95.47	6.263%	$101.4493	$101.45	$101.45	$101.40
Purchase #5	$78.56	6.686%	$83.8125	$83.81	$83.80	$83.80
Purchase #6	$24.52	13.282%	$27.7767	$27.78	$27.80	$27.80
Purchase #7	$208.93	10.320%	$230.4916	$230.49	$230.50	$230.50
7 purchase totals =	$546.24		$594.1896	$594.19	$594.25	$594.10