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	$215.74	11.245%	$240	$240.00	$240.00	$240.00
Purchase #2	$83.47	7.835%	$90.0099	$90.01	$90.00	$90.00
Purchase #3	$134.65	9.129%	$146.9422	$146.94	$146.95	$146.90
Purchase #4	$244.71	10.241%	$269.7708	$269.77	$269.75	$269.80
Purchase #5	$183.49	7.611%	$197.4554	$197.46	$197.45	$197.50
Purchase #6	$19.78	9.352%	$21.6298	$21.63	$21.65	$21.60
Purchase #7	$37.35	13.844%	$42.5207	$42.52	$42.50	$42.50
7 purchase totals =	$919.19		$1,008.3288	$1,008.33	$1,008.30	$1,008.30