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	$237.53	9.134%	$259.226	$259.23	$259.25	$259.20
Purchase #2	$204.51	3.852%	$212.3877	$212.39	$212.40	$212.40
Purchase #3	$103.74	4.862%	$108.7838	$108.78	$108.80	$108.80
Purchase #4	$77.77	5.457%	$82.0139	$82.01	$82.00	$82.00
Purchase #5	$80.60	12.269%	$90.4888	$90.49	$90.50	$90.50
Purchase #6	$209.42	4.868%	$219.6146	$219.61	$219.60	$219.60
Purchase #7	$93.52	9.317%	$102.2333	$102.23	$102.25	$102.20
7 purchase totals =	$1,007.09		$1,074.7481	$1,074.74	$1,074.80	$1,074.70