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	$27.46	4.782%	$28.7731	$28.77	$28.75	$28.80
Purchase #2	$189.53	12.631%	$213.4695	$213.47	$213.45	$213.50
Purchase #3	$27.60	13.810%	$31.4116	$31.41	$31.40	$31.40
Purchase #4	$109.70	3.788%	$113.8554	$113.86	$113.85	$113.90
Purchase #5	$174.37	9.521%	$190.9718	$190.97	$190.95	$191.00
Purchase #6	$218.51	13.568%	$248.1574	$248.16	$248.15	$248.20
Purchase #7	$222.90	8.172%	$241.1154	$241.12	$241.10	$241.10
7 purchase totals =	$970.07		$1,067.7542	$1,067.76	$1,067.65	$1,067.90