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	$96.81	3.432%	$100.1325	$100.13	$100.15	$100.10
Purchase #2	$90.97	11.407%	$101.3469	$101.35	$101.35	$101.30
Purchase #3	$28.67	10.284%	$31.6184	$31.62	$31.60	$31.60
Purchase #4	$174.78	7.866%	$188.5282	$188.53	$188.55	$188.50
Purchase #5	$103.72	7.531%	$111.5312	$111.53	$111.55	$111.50
Purchase #6	$183.26	11.618%	$204.5511	$204.55	$204.55	$204.60
Purchase #7	$65.69	12.709%	$74.0385	$74.04	$74.05	$74.00
7 purchase totals =	$743.90		$811.7468	$811.75	$811.80	$811.60