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	$234.31	9.109%	$255.6533	$255.65	$255.65	$255.70
Purchase #2	$39.90	5.557%	$42.1172	$42.12	$42.10	$42.10
Purchase #3	$82.86	9.369%	$90.6232	$90.62	$90.60	$90.60
Purchase #4	$72.36	6.365%	$76.9657	$76.97	$76.95	$77.00
Purchase #5	$180.48	13.632%	$205.083	$205.08	$205.10	$205.10
Purchase #6	$216.80	11.349%	$241.4046	$241.40	$241.40	$241.40
Purchase #7	$150.67	10.575%	$166.6034	$166.60	$166.60	$166.60
7 purchase totals =	$977.38		$1,078.4504	$1,078.44	$1,078.40	$1,078.50