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	$20.64	3.781%	$21.4204	$21.42	$21.40	$21.40
Purchase #2	$139.72	6.532%	$148.8465	$148.85	$148.85	$148.80
Purchase #3	$72.76	12.780%	$82.0587	$82.06	$82.05	$82.10
Purchase #4	$87.44	13.800%	$99.5067	$99.51	$99.50	$99.50
Purchase #5	$95.31	9.135%	$104.0166	$104.02	$104.00	$104.00
Purchase #6	$205.83	10.455%	$227.3495	$227.35	$227.35	$227.30
Purchase #7	$200.46	7.773%	$216.0418	$216.04	$216.05	$216.00
7 purchase totals =	$822.16		$899.2402	$899.25	$899.20	$899.10