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	$29.72	4.166%	$30.9581	$30.96	$30.95	$31.00
Purchase #2	$66.97	7.611%	$72.0671	$72.07	$72.05	$72.10
Purchase #3	$111.41	8.109%	$120.4442	$120.44	$120.45	$120.40
Purchase #4	$115.95	6.551%	$123.5459	$123.55	$123.55	$123.50
Purchase #5	$63.67	13.750%	$72.4246	$72.42	$72.40	$72.40
Purchase #6	$92.77	9.771%	$101.8346	$101.83	$101.85	$101.80
Purchase #7	$77.64	6.573%	$82.7433	$82.74	$82.75	$82.70
7 purchase totals =	$558.13		$604.0178	$604.01	$604.00	$603.90