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	$198.86	9.170%	$217.0955	$217.10	$217.10	$217.10
Purchase #2	$46.92	5.781%	$49.6324	$49.63	$49.65	$49.60
Purchase #3	$244.83	4.659%	$256.2366	$256.24	$256.25	$256.20
Purchase #4	$89.37	13.794%	$101.6977	$101.70	$101.70	$101.70
Purchase #5	$41.32	8.607%	$44.8764	$44.88	$44.90	$44.90
Purchase #6	$78.97	13.364%	$89.5236	$89.52	$89.50	$89.50
Purchase #7	$97.57	3.301%	$100.7908	$100.79	$100.80	$100.80
7 purchase totals =	$797.84		$859.8530	$859.86	$859.90	$859.80