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	$202.64	12.520%	$228.0105	$228.01	$228.00	$228.00
Purchase #2	$58.60	12.213%	$65.7568	$65.76	$65.75	$65.80
Purchase #3	$66.73	10.646%	$73.8341	$73.83	$73.85	$73.80
Purchase #4	$119.54	6.619%	$127.4524	$127.45	$127.45	$127.50
Purchase #5	$67.52	4.280%	$70.4099	$70.41	$70.40	$70.40
Purchase #6	$117.38	9.868%	$128.9631	$128.96	$128.95	$129.00
Purchase #7	$108.82	13.752%	$123.7849	$123.78	$123.80	$123.80
7 purchase totals =	$741.23		$818.2117	$818.20	$818.20	$818.30