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	$96.80	3.146%	$99.8453	$99.85	$99.85	$99.80
Purchase #2	$114.35	10.692%	$126.5763	$126.58	$126.60	$126.60
Purchase #3	$178.81	11.753%	$199.8255	$199.83	$199.85	$199.80
Purchase #4	$220.49	4.589%	$230.6083	$230.61	$230.60	$230.60
Purchase #5	$40.95	4.676%	$42.8648	$42.86	$42.85	$42.90
Purchase #6	$15.73	5.555%	$16.6038	$16.60	$16.60	$16.60
Purchase #7	$121.56	5.421%	$128.1498	$128.15	$128.15	$128.10
7 purchase totals =	$788.69		$844.4738	$844.48	$844.50	$844.40