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	$83.80	7.661%	$90.2199	$90.22	$90.20	$90.20
Purchase #2	$219.73	12.171%	$246.4733	$246.47	$246.45	$246.50
Purchase #3	$60.29	9.236%	$65.8584	$65.86	$65.85	$65.90
Purchase #4	$160.52	13.703%	$182.5161	$182.52	$182.50	$182.50
Purchase #5	$172.62	5.534%	$182.1728	$182.17	$182.15	$182.20
Purchase #6	$212.35	13.513%	$241.0449	$241.04	$241.05	$241.00
Purchase #7	$89.92	3.732%	$93.2758	$93.28	$93.30	$93.30
7 purchase totals =	$999.23		$1,101.5612	$1,101.56	$1,101.50	$1,101.60