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	$20.91	4.113%	$21.77	$21.77	$21.75	$21.80
Purchase #2	$125.31	6.553%	$133.5216	$133.52	$133.50	$133.50
Purchase #3	$164.82	12.756%	$185.8444	$185.84	$185.85	$185.80
Purchase #4	$81.46	12.704%	$91.8087	$91.81	$91.80	$91.80
Purchase #5	$175.35	3.104%	$180.7929	$180.79	$180.80	$180.80
Purchase #6	$183.35	9.604%	$200.9589	$200.96	$200.95	$201.00
Purchase #7	$129.82	11.632%	$144.9207	$144.92	$144.90	$144.90
7 purchase totals =	$881.02		$959.6172	$959.61	$959.55	$959.60