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	$91.80	12.836%	$103.5834	$103.58	$103.60	$103.60
Purchase #2	$91.62	7.854%	$98.8158	$98.82	$98.80	$98.80
Purchase #3	$108.86	13.582%	$123.6454	$123.65	$123.65	$123.60
Purchase #4	$111.84	5.199%	$117.6546	$117.65	$117.65	$117.70
Purchase #5	$208.57	4.199%	$217.3279	$217.33	$217.35	$217.30
Purchase #6	$83.90	8.223%	$90.7991	$90.80	$90.80	$90.80
Purchase #7	$126.71	3.620%	$131.2969	$131.30	$131.30	$131.30
7 purchase totals =	$823.30		$883.1231	$883.13	$883.15	$883.10