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	$74.58	9.864%	$81.9366	$81.94	$81.95	$81.90
Purchase #2	$88.52	8.259%	$95.8309	$95.83	$95.85	$95.80
Purchase #3	$74.72	5.519%	$78.8438	$78.84	$78.85	$78.80
Purchase #4	$93.93	10.178%	$103.4902	$103.49	$103.50	$103.50
Purchase #5	$115.46	7.376%	$123.9763	$123.98	$124.00	$124.00
Purchase #6	$203.40	6.232%	$216.0759	$216.08	$216.10	$216.10
Purchase #7	$164.83	3.289%	$170.2513	$170.25	$170.25	$170.30
7 purchase totals =	$815.44		$870.4050	$870.41	$870.50	$870.40