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	$33.55	11.563%	$37.4294	$37.43	$37.45	$37.40
Purchase #2	$138.77	9.700%	$152.2307	$152.23	$152.25	$152.20
Purchase #3	$31.67	10.118%	$34.8744	$34.87	$34.85	$34.90
Purchase #4	$86.94	4.193%	$90.5854	$90.59	$90.60	$90.60
Purchase #5	$38.58	11.417%	$42.9847	$42.98	$43.00	$43.00
Purchase #6	$158.66	3.855%	$164.7763	$164.78	$164.80	$164.80
Purchase #7	$94.59	3.641%	$98.034	$98.03	$98.05	$98.00
7 purchase totals =	$582.76		$620.9149	$620.91	$621.00	$620.90