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	$56.34	6.231%	$59.8505	$59.85	$59.85	$59.90
Purchase #2	$132.87	10.514%	$146.84	$146.84	$146.85	$146.80
Purchase #3	$147.40	3.686%	$152.8332	$152.83	$152.85	$152.80
Purchase #4	$29.43	7.461%	$31.6258	$31.63	$31.65	$31.60
Purchase #5	$164.28	11.565%	$183.279	$183.28	$183.30	$183.30
Purchase #6	$240.26	9.320%	$262.6522	$262.65	$262.65	$262.70
Purchase #7	$97.90	5.344%	$103.1318	$103.13	$103.15	$103.10
7 purchase totals =	$868.48		$940.2125	$940.21	$940.30	$940.20