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	$54.32	5.308%	$57.2033	$57.20	$57.20	$57.20
Purchase #2	$103.33	10.610%	$114.2933	$114.29	$114.30	$114.30
Purchase #3	$90.45	11.482%	$100.8355	$100.84	$100.85	$100.80
Purchase #4	$143.71	11.645%	$160.445	$160.45	$160.45	$160.40
Purchase #5	$250.52	4.378%	$261.4878	$261.49	$261.50	$261.50
Purchase #6	$78.72	4.525%	$82.2821	$82.28	$82.30	$82.30
Purchase #7	$115.52	9.768%	$126.804	$126.80	$126.80	$126.80
7 purchase totals =	$836.57		$903.3510	$903.35	$903.40	$903.30