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	$242.39	5.626%	$256.0269	$256.03	$256.05	$256.00
Purchase #2	$158.69	6.270%	$168.6399	$168.64	$168.65	$168.60
Purchase #3	$93.28	10.590%	$103.1584	$103.16	$103.15	$103.20
Purchase #4	$87.69	3.408%	$90.6785	$90.68	$90.70	$90.70
Purchase #5	$112.88	9.704%	$123.8339	$123.83	$123.85	$123.80
Purchase #6	$81.66	12.107%	$91.5466	$91.55	$91.55	$91.50
Purchase #7	$144.72	11.294%	$161.0647	$161.06	$161.05	$161.10
7 purchase totals =	$921.31		$994.9489	$994.95	$995.00	$994.90