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	$243.38	7.851%	$262.4878	$262.49	$262.50	$262.50
Purchase #2	$86.65	3.801%	$89.9436	$89.94	$89.95	$89.90
Purchase #3	$169.68	9.592%	$185.9557	$185.96	$185.95	$186.00
Purchase #4	$5.47	6.361%	$5.8179	$5.82	$5.80	$5.80
Purchase #5	$192.63	12.564%	$216.832	$216.83	$216.85	$216.80
Purchase #6	$74.79	7.125%	$80.1188	$80.12	$80.10	$80.10
Purchase #7	$131.30	6.210%	$139.4537	$139.45	$139.45	$139.50
7 purchase totals =	$903.90		$980.6095	$980.61	$980.60	$980.60